There is no finer tool for finding that which is hidden than the good old Compass! While the basic Compass is good for general work, there are a few as-of-yet untapped areas of tracking available.
1: Rouge's Compass
For the Heros that like to hunt for secrets, this compass is for you! Revealing all breakable/invisible doorways on your map, and playing a special tone when you enter a room that has one you've not yet gone through.
2: Dowsing Rod
A more curious compass than most, the Dowsing Rod seems to target a (seemingly) random spot or object elsewhere in the dungeon, constantly pointing towards it at all times, even when it's on a different floor entirely! The actual target is, of course, up to the maker's discretion.
3: Hunter's Mark
No creature is safe while you have this on hand! Each Hunter's Mark is targeted to a specific number of a specific monster. Once you have defeated the required amount, a new point of interest is highlighted on your map! (Again, both designated by the dungeon maker)