Gloom Castles is a Capture the Flag conversion of one of the original shareware Quake levels, Gloom Keep. The original level wasn't particularly suited to deathmatch play due to its linear structure and layout, filled with cramped corridors and complex rooms, but is perfectly suited to the gameplay style of Capture the Flag.

The conversion is ‘not an official id product or release,’ but was undertaken by the original designer, Tim Willits, along with some assitance from other id staff members John Cash and Christian Antkow, and Steve Tietze of Rogue Entertainment.

There are actually several distinct versions of the map, but the differences are insignificant. The original release was as IDCTF1, but it also appears in the second Threewave CTF episode as CTF2M7.