Realm Brew: Open Underground Set

This set includes 18 open tiles each with a light side and a dark side, all with the 1-inch grid, and comes with a complete set of Fog of War Tiles to keep your maps a mystery until the adventure unfolds.

The light side can be used to make large open areas inside a cave or as a standalone open map which you can mark up as you wish. 

The dark side can be used in the same way, to represent large dark areas. It can also be used to fill in and connect open areas of the map. This can not only reinforce the map, it can also allow openings for travelling through underground areas, if that's via magic or tunnelling through. It can also be a great base layer if you want to build multilevel dungeons!