The £3.3m tree house at Alnwick Garden has officially opened to the public, but Alix got the chance to test out the building before anyone else. She tells us what it's like to be in one of the biggest tree houses in the world.
"I wanted to try out the tree house because it looked really great.
It was actually really fun and it looked like it cost a lot of money to build.
It's quite dark inside, but it's got a fireplace in the middle of the main room.
The tree house also has a party room at the top and the toilets are at the top of the building.
Lots of space
The party room had wooden chairs and wooden tables. It had two doors that lead to a balcony.
In the party room you can eat, play, and dance about. There's a lot of space.
The café is really, really big and the seats are made of tree bark. They served sandwiches, apples, cakes and biscuits.
I liked the swingy bridges - when you're at one end and another person's at the other, you can start jumping and the other person starts bouncing up and down!
The tree house is a good place for family and it's really fun.
I think more people will come in the summer because it'll be a lot drier and sunnier.
A lot of people come to Alnwick Gardens and now that the tree house has been built I think it will attract more people. I'll visit it quite often."
Alix, 9, Alnwick