How do I make it so once a part is touched, another part appears?

I just wondered whether anybody could help me with my problem, in my game I’m working on I’d like to make it, once you have touched one part another part appears and becomes available, the game is that you spawn in a public toilet and discover a crack in the wall, the only problem is, is that I want people to go into the crack in the wall before they go into a toilet stall and teleport into the sewers! Let me know if you can help!