Press Packers Charlotte, 10, and Patrick, 13, travelled from London to Mount Everest - the tallest and most famous mountain in the world.
But the pair - who are sister and brother - weren't just on holiday.
They were taking part in a study to help doctors find new ways of helping children who have breathing problems.
They reported back to Newsround every step of the way with this online diary.
Wednesday 9 May - Back home
"Hello from Charlotte! I have now been back home from our trip to Nepal for three weeks.
The first thing I did when I got back was have a bath and some pizza.
We got back on Sunday evening and I had to go to school straight away on the Monday!
And the first week I got back I kept waking up really early due to the time difference.
It was great to see my friends again, even though some of the boys in my class called me a guinea pig and a lab rat because of all the medical testing we did!
Charlotte, Patrick and some of the team high up in the Himalayas
My favourite bits of the trip were seeing all the wildlife and knowing I was in the Himalayas.
My dad is still there helping with the adult medical study so now I am look forward to him coming back from Nepal too.
We had the experience of a lifetime in Nepal and I would love to go again hopefully when I'm older!"
Saturday 7 April - Easter disappointments
"Hi it's Charlotte here - and we are now back in Namche.
We arrived back today and I was surprised to be met by my mum - she had been walking higher up with Patrick but he had got a bad headache at Lobouche (4,900m) and so they had to come down.
Patrick was upset because he was not allowed to go any higher because of this, even though Everest Base Camp was only 400m higher.
But one of the scientists, Aiden, also had a headache and had to come down so that made him feel a lot better!
Every night we've been staying in lodges with small rooms with very thin walls like cardboard.
And don't get me started on the loos! They are holes in the ground.
I know they are environmentally-friendly but I don't like them. You have to hold your nose when you go in!
I can't remember the last time I had a shower.
It gets very cold at night and more so the higher up the mountains you go. The highest we got was Tengboche (3,800m).
It is Easter Sunday tomorrow but we don't have any chocolate eggs which I am cross about!
Most of the people here are Buddhists and don't celebrate Easter so we'll just have some normal chocolate bars instead."
Sunday 1 April - April Fool!
"It's Charlotte again! We are still having lots of fun in Namche - the village where the medical base is.
And the food is lovely - noodle soup, chapattis, rice - but all a bit spicy!
We've been getting up early - 4.30am one day and 5.30am another. It is still really cold then.
It has been lovely and warm during the day but freezing at night.
When we are trekking it gets hot but we have lots of rests.
And if we get really tired, the sherpas (who are the porters/guides with us) carry our rucksacks. Sometimes even the younger children get carried themselves - lucky them!
We are still doing medical tests every day but now we are higher in the mountains it is getting harder to breathe when we do the exercises.
We can see Everest from here and also an amazing mountain called Ama Dablam.
As today is April's Fool Day we painted on our cousin William's face at 2.30am whilst he was asleep!
Tomorrow we leave for our next base - I can't wait!
But I am missing home a bit, especially my friends (hello Izzy and Emma). And I'd love to eat some chips!"
Friday 30 March - Heading higher and higher
"Hello from Lottie! The trek from Kathmandu was tiring but we saw some beautiful sights as we walked higher.
We had to go over some quite scary rope bridges but we also saw Everest on the final walk up to our next base.
It looked amazing!
When we got to Namche Bazaar I was also really excited as I finally saw my Dad again. This is where he is working and testing adults for the medical study.
We've done some more medical tests up here but I think we are now going to go to a nearby market.
I'm missing home a bit but it is wonderful here."
"Hi, it's Patrick again. After doing a difficult walk, going higher and higher (from a height of 2800m to 3400m), we have arrived at our next base which is called Namche Bazaar.
The team trekking uphill
The last day and a half we've been acclimatising, enjoying the sunshine and getting used to being at a high altitude laboratory where they are doing the medical tests.
And we've been doing more testing, like we did when we first got to Kathmandu.
Yesterday, I saw Mount Everest for the first time and it made me feel really excited knowing I'm going to trek to it!
Tomorrow we will be walking up another 500m so I hope we will get even better views of it.
And then we will be walking to Tengboche and going to a place called Kalapathar which is even higher, at 5545m, which is meant to have great views of Everest!
I still really hope that I can trek to Everest Base Camp. This would be the highest place I can go before it gets too dangerous for my age as there will be far less air - I will keep you posted!"
Monday 26 March - We've arrived!
"Hello from Lottie - I'm now in Kathmandu which is the capital of Nepal.
We arrived on Sunday and have already have seen some sights and some monkeys, which made everyone laugh!
So far, I've enjoyed everything - especially the Nepalese dinner last night. The rice and chips were yummy!
Today I've done lots of tests and had a swim which was fun. It's all been amazing so far and can't wait for more."
"Hi, it's Patrick here! We all arrived safely with loads of luggage in Kathmandu and we are already enjoying the culture and food.
Patrick does a breathing test
Last night, we had a traditional Nepalese meal - I tried roasted boar!
We have been spending today testing - memory tests and breathing tests. We have to do these every day.
The doctors want to see if anything changes when we go higher in the Himalayas where there is less air.
But we managed to fit in a bit of sightseeing too!
Tomorrow we will be starting the trek. First we fly to a place call Lukla and then start to trek to Phakding - I hope to tell you more soon!"
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