The MPLogu's Underground-Cave POI Collection is a great collection of underground and cave POI. There are seven different prefabs: the Petra/Indiana Jones Temple, the Skywalker Homestead, Skeletor's Hermitage, Rave Cave, Rad Cave, and Rainbow Cave. These prefabs include customized blocks, so they must be installed as a mod (instructions below).

To install this mod pack, unzip the downloaded file into either your appdata Mods folder (see illustration in the photo gallery) or into your game's Mod folder.

To find your appdata folder, open up your File Explorer, and type %appdata% in the address bar at the top.