Quake Episode 5: Dimension of the Past

Dimension of the Past (called "DOPA" for short) is an add-on episode for Quake developed by MachineGames, to commemorate the game's 20th anniversary. It's available to download for free, and was also included in the modern Quake port.

Despite not being developed by id Software themselves, the episode is officially released in the 2021 release, being developed by a fellow Zenimax-owned company that has previously co-operated with id Software as well as Nightdive Studios. The episode also contains many allusions and callbacks to Quake proper, such as the re-appearance of the Dopefish easter egg, along with the final level of the episode being almost identical to Shub-Niggurath's Pit.