Matthew from Essex won our competition to go and see a special iMax screening of Harry Potter and the Prisoner of Azkaban at the Science Museum in London.
He also got to take part in a sleepover there with his friends.
"We arrived at the Science Museum in London and the first thing we did was have our photos taken in our costumes for a competition.
I went dressed as a wizard in a cloak with a hat and a wand. There were about 100 people there in total.
Then we went through and watched Harry Potter and the Prisoner of Azkaban in the iMax cinema which has a really big screen!
It was much better than in a normal cinema and much scarier because it was so much bigger. The bit when the dementors come onto the Hogwarts Express was really scary!
Sleeping in space!
After the film they announced the winners of the fancy dress competition - there were two joint winners who were brothers and were dressed up as Fred and George, they looked really good.
We went to look at where we were sleeping - I slept in the space gallery. The lights went off at midnight. After the lights went off lots of people were jumping around in their sleeping bags and stuff.
It was quite cosy in the sleeping bags, but I only had about four hours sleep! In the morning they switched on the lights - most people were awake already, but one of my friends Oliver stayed asleep even after the lights were switched on!
Bubbles and slime!