Den (noun)

1. A wild animal's lair or shelter.
2. A small, cramped, and uncomfortable room.
3. A place where people engage in a particular activity, especially a criminal or illegal one.
4. A private room or space in a larger building, especially one used for a particular purpose.

Origin:

Middle english: from old english denn; related to dutch and german tenne 'threshing floor', also to dungeon.

Examples:

1. The den of the lion was found in the dense jungle.
2. The prisoner was locked up in a dark and damp den.
3. The police raided the den where illegal drugs were being sold.
4. The den was used as a secret meeting place by the group.
5. The artist had a cozy den in the attic where she would paint for hours.