Large trap door - alternative to door with frame 4595708
This hinge combined with a technic pin lets you easily make large trap doors. You can see a train-track-sized trap door in this model using two of these parts. In this model the trap door falls down when you retract an axle that normally holds it up. Other arrangements are possible.

The beauty of this particular hinge is that it is symmetrical, so there aren't two different halves to keep track of, and you can use any kind of technic pin you want. The relatively long plate on it makes it sturdier than some of the older variants like this one.