The Underworld framework has been developed to produce a suite of tools that can be used by researchers to simulate large-scale earth processes, such as plate/mantle interaction and basin development. The Underworld collection details the core set of phenomena modelled and distributed with Underworld, including lithospheric deformation, slab subduction, mantle convection, heat flow at the regional scale, crustal heat transport by fluid flow at low temperature, a hot-dry rock simulator and geothermal, multiphase-fluid-transport engineering models. The collection also includes a suite of benchmarks and verification models.