Collision and Triggers

Seems like a simple question but I figured I'd ask before the time comes to code and I have no idea what to do- Basically for our FFP, we are going to have a room with a door. The player will have to hit a switch (either jump on, use a keyboard key, etc.) to open the door after killing some enemies.

My question is, how would I code collision detection for the "door" object so the player cannot run through it and how would I go about coding a trigger for the switch (I was thinking of just destroying the door or having it move?)? Thanks.