Aymeric. Visits to the underground caves created by lava in the Grand Brûlé area, also called lavatubes. Because lava tubes remain buried, often not recognized in the surface. However, many lava tubes are delineated on the surface by a series of linear or curvilinear collapse depressions, called ventilation holes along the tube axis. In active lava tubes, skylights provide a unique insight into the actively flowing hot lava in the lava tube system.