Hide a room or item - make it invisible until game master reveals it

This would be a great feature, we are playing with a map shared on a screen, we base a lot of ''perception'' rolls, based on which you can find additional objects, secret rooms, quest items and all sorts of hidden stuff. If I show a map where people can quickly figure out the content just based on shape and visible rooms in the distance, makes no sense - they shouldn't know what's in there until they reveal it.

It makes exploration a completely different experience!