Precursor Dungeons are microdungeons found rarely on the surface and/or underground of certain planets. Finding one of these is very rewarding though, as they could contain advanced technology, such as the Erchius Converter, which converts most fuels to Precursor Quantum Fluid, which in turn can be converted to Ancient Essence or the Cosmic Crucible, which uses Ancient Essence to upgrade your gear to potentially tier 8. Other things of note potentially found are chests containing Precursor ingredients and other related items. Precursor Dungeons almost always contain traps or guards.

As of september 15 2017, the Precursor Microdungeon is moved to its own biome; the aptly named Precursor Biome, which is recognizable by its black and yellow metallic blocks and the robotic enemies. These biomes have a chance to appear on the more difficult planet types, but have a preference to Cybersphere planets. They can either appear at the surface level or all of the underground levels except the core. Note that while these biomes can appear regularly, the actual Precursor dungeon is a very rare occurrence. So finding a Precursor biome is definitely not a guarantee for finding a dungeon. However, these biomes can be used as an indicator that one of these dungeons could be nearby

In previous versions of Frackin Universe, these dungeons did not have their own biome and could appear on many other biomes. This made finding them more a matter of luck than actually knowing where to look.

Precursor Dungeons do not feature any kind of tile protection, so they can be broken down for their parts or items. The sole exception being the Cosmic Crucible. Both the tiles below it and the anvil itself are impervious to any attempts to remove it.

The Precursor Biome (and possibly the dungeon) can be found on the surface at the following planets:

They can be found underground on:

*= Includes Dark variants.