Wow, what an amazing day. Definitely the highlight of Hawaii so far, by miles. Let me start from the beginning.

We took breakfast this morning in the Coconut Grill next door to the hotel. It is complimentary during our stay, and there were three options. 1) The healthy choice - consisting of oatmeal, papaya, banana bread and yoghurt. 2) Flap Jack Griddle - which is actually pancakes with ham and scrambled eggs. 3) Locals breakfast - consisting of eggs, sausage/ham/bacon, rice/fries and toast. Stu was very good and opted for the healthy choice, but I couldn't resist the pancakes as I was really hungry - I can be healthy tomorrow! Stu's breakfast looked really nice, whereas mine looked like a heart attack on a plate! It was two really fat pancakes, with a whole layer of scrambled eggs on top, a wedge of bacon in the middle and then maple syrup to pour over. Oh, and a healthy wedge of papaya on the side just to balance it out! My breakfast was quite nice, but incredibly filling. I think I'll have to opt for the healthy option tomorrow for the sake of my cholesterol level!

We had first decided that today we would take a drive down the Chain Of Craters road, to see what we could see of the volcano and other sights along the way. We thought that tomorrow we could take a trip to Mauna Kea - to see the observatories and do start gazing at the top of a dormant volcano. However, when we checked the weather report for Mauna Kea it seemed that from tomorrow the clouds would be moving in with lots of rain, and so the visibility would not be good. We realised that our only real chance to get a good day, was today!

You can drive up to the Visitor Centre which is at an elevation of around 9,000 feet, but from here to the summit you will need a four-wheeled drive. You can join a tour which will take you up to the summit in their own four-wheeled drive, but when we looked up the prices it was well over $200 each! We decided to see how much it would be to rent a four-wheeled drive vehicle ourselves, and were delighted to hear it would only cost just under $130. This would be great, as not only would it be cheaper but we could take things at our own pace, rather than follow someone else's schedule.

A quick call to the car rental company up the road, and 20 minutes later we were driving out of the rental place with our very own seven seated SUV four-wheeled drive, which we'd rented for the day.

We made a quick stop back at the hotel to pick up a few bits and bring along some warmer clothes - the summit can get down to freezing temperatures. Then we made a stop at a supermarket to pick up some sandwiches and snacks to last us the rest of the day - we wouldn't be returning to the hotel until late evening as we would stay up there for the stargazing, so we needed to make sure we had enough food and water.

To get to the Mauna Kea access road we had to drive west from Hilo, more or less half way across the island - although this only took around half an hour. At the bottom of the access road we actually missed the turning first of all to the access road. However, this proved to be a good thing, because when we drove back on the other side of the road we noticed a huge area of old solidified lava flows. We got out of the car to get a better look.

It was quite amazing walking over the solidified lava flow. You could see some of the ripples and waves that were in the lava as it hardened. There were also some large cracks in it, and even some giant holes. Some of the thinner pieces of rock would crumble under your feet at it was so brittle. It was amazing to walk over it though, a new experience for both of us.

After taking lots of pictures we got back into the car and took the access road to Mauna Kea. The access road as far as the Visitor Centre is an ascent of 9,000 feet and then up to nearly 14,000 at the summit! Due to the high altitude there are some important rules to follow and lots of safety information to read. The big thing to take notice of is the warning to stay at the Visitor Centre for at least half an hour, before continuing onwards. This is so your body can adjust to the altitude, and will greatly reduce your chances of suffering any of the symptoms of altitude sickness further up.

The drive up to the Visitor Centre alone is fantastic. You ascend fairly quickly, and the view becomes amazing straight away. However, the truly amazing part comes when you reach the clouds. Actually driving through and above the clouds is fantastic, yet also quite surreal. This is a view you only normally see when flying in a plane, so seeing it out the side of your car window is something else entirely.

We arrived at the Visitor Centre around 2:30pm. We took a look inside where they had some interesting posters and information about Mount Kea and also some astrological information. We watched a video inside which they had on a constant loop, which gave a bit of background about the volcano. Then we sat outside in the sun and had a bite to eat. We knew we had all afternoon and evening, and we wanted to be around for sunset and the evening's stargazing, so we were able to take things very easy.

After some food we spoke to one of the staff members inside, just to check what time sunset would be and if he could recommend any other things to do. He said that there were a couple of small hikes once at the summit, so factoring in the time it takes to get up there too, we decided to head up.

A bit of information about Mauna Kea:

Mauna Kea is about a million years old and last erupted between 4,000 and 6,000 years ago, so is now considered to be dormant. It stands at 13,796 feet above sea level, and has the highest peak in the state of Hawaii. However, most of the mountain is under water, so when measured from its oceanic base Mauna Kea is over 33,000 feet tall - significantly taller than Mount Everest.

In Hawaiian mythology, the peaks of Mauna Kea are considered to be the most sacred of all peaks on the Hawaiian islands.

With its high altitude and dry environment, Mauna Kea's summit is one of the best sites in the world for astronomical observation. Since the creation of an access road in 1964, thirteen telescopes have been constructed at the summit. The Mauna Kea Observatories are used for scientific research across the electromagnetic spectrum from visible light to radio, and comprise the largest such facility in the world.

We had a further eight miles to travel and around 5,000 feet to ascend up Mauna Kea to the summit. We decided to take it nice and slow, as we were in no hurry and were also aware of the effects being at such high altitudes can have on your body.

The drive was great, and we were treated to even more amazing views along the way. The road was a series of switchbacks, and we had to take it slow due to the ascent, and also because of most of it being gravel.

We could just about see the summit above us, but decided to take a stop. Stu was starting to feel a bit light-headed, and I was starting to get a bit of a headache too. We thought a stop might help us adjust a bit better.

After sitting there for ten minutes or so, Stu was unsure if he could continue up. So we decided to drive a little way back down the road to the next stop-off point, just to see if Stu felt a bit better.

Going further down did have a positive effect. We both felt better and Stu was feeling confident again to start driving up to the summit. But we made sure we took it really easy and slow. We drove just as far as we went before and stopped here again for a while. After a few more minutes we were both feeling better and felt ready to go to the top.

We were soon passing mountainsides which had huge chunks of ice and snow on them, and eventually made it to the loop road at the top. Here we were able to drive around to each side of the summit and stop to look and take pictures.

The view off the summit was incredible, it's hard to describe just what an amazing feeling it was to be at 14,000 feet, sitting in our car and looking out and over the edge. We also remembered that when we did our skydive back in Australia a couple of years ago, we did that from 14,000 feet!

At the summit are the huge observatories and telescopes. Unfortunately these are not open to the public unless you come on the organised tour on the weekend, but we couldn't have made that anyway - plus the weather is supposed to be terrible then. We weren't disappointed though as there was plenty to see up here.

The guy at the Visitor Centre had told us about a couple of trails we could take while up here. However, whilst we were feeling better than before we were still feeling the effects of the high altitude. Stu said that just jumping out the car, taking some pictures, then walking back to the car was making him feel really tired. We decided that a hike might not be the best idea. I think we were just glad we'd actually made it to the summit!

After being at the summit for at least half an hour, Stu wanted us to drive back down to the stop off point we went to earlier, just to recover a bit from the altitude. We stayed down there for half an hour or so, and then made our way back to the summit once again in time for sunset.

We noticed that suddenly a lot of tour groups arrived at the summit ready to watch the sunset. We were so glad we did this by ourselves and didn't book a tour. It not only meant we saved a lot of money, but it meant we could adjust to the altitude at our own pace. I overheard someone later on talking about a person that had been on one of these tour buses, and she said they kept having to stop for people to be sick on the way up! Doesn't sound pleasant.

At the top it was now getting really cold - the temperature must have been around zero. We had our fleeces, hats and gloves on and were still cold! We saw one guy in shorts and t-shirt - he must have been absolutely freezing!

After witnessing an amazing sunset, with colours bursting right across the sky, we drove back down to the Visitor Centre for some stargazing.

Once down there we could see that they had a few of the telescopes already set up outside. There were a couple pointed at the moon. We looked through one of these and it was superb - you could see the moon so close up and see each individual crater. We got chatting to the guy operating the telescope (I think he said his name was Cliff Livermore) and he adjusted it so we could look at Jupiter too. We could actually make out the cloud patterns going across Jupiter, it was amazing! We also got to see the Andromeda galaxy - apparently the furthest thing away from us that we can see in the night sky.

Cliff also told us that the BBC had been here recently to film a programme about the observatory here on the mountain. Cliff said he was in it too. My brother told me he had watched a programme on TV the other day about the observatory, so I assume that the one he was talking about.

After grabbing a quick hot drink from inside, Cliff called everyone over for his stargazing talk. Here he pointed out, with the use of a very fancy laser, all the constellations in the sky. I have to say I totally loved it, it was really interesting, and Cliff had a good sense of humour too which always helps. I've always wanted to have the constellations pointed out to me properly, and now I have.

This has certainly been our favourite day in Hawaii so far - and I would say a big highlight of our whole trip so far too. We thoroughly enjoyed it - even though Stu suffered a bit with the altitude. I reckon this just made it even more of a great achievement upon reaching the top.

Cliff began showing some of the other stars and planets we had already seen earlier, so we decided to head off back to the hotel. Driving down the mountain was ok in the dark, but once we were off the access road at the bottom, the road back to Hilo was filled with thick fog. It was an eery drive back, but all part of the experience.

Stu had a conference call for work when we got back, which was a shame as we were both feeling extremely tired after today. Luckily the call didn't last too long, and we soon went to bed after an amazing day!