I found out how to do it. Just writing how I did it so other people dont have to make new threads:
I kept the room, but made no way to go in it. (That means there should be absolutley no way to go in it with the compass direction, or "go to", out etc.)
I made a new object, a door.
The thing you have to open the door with (in my case, the tickets):
- First, you go to Inventory tab for the object you wanna use on the door;
- Click Edit "use" details...;
- Click on Use (the object) on its own;
- Click add at Objects that (the object) can be used on;
- When the box pops up, click the arrow to scroll down and pick the door;
- When the SECOND box pops up, click Modify;
- Then click Modify south exit, north exit or where ever you want it;
- Where it says "From room", put there any room (in my case, the hallway);
- Where it says "To room", put there the room you made, the one that you cant go in without using that object;
- Save the game;
- Enjoy!

I hope this is useful for others