Unlike most other locations, the location of Terra Cave is not set at all; it can be determined by speaking with a man at Hoenn's Weather Institute, who will explain that one of four routes is under abnormal weather conditions. If the player does not reach Terra Cave fast enough, it will temporarily disappear and Marine Cave will appear. However, once Kyogre is battled/caught in Marine Cave, or if the player did not arrive there fast enough, Terra Cave will reappear and relocate. It is able to appear in places as far from each other as Route 115 and Route 118, though it mostly sticks to the western side of Hoenn. In Pokémon Emerald, it is the only place where Groudon can be caught. It will only appear once the Hoenn Elite Four have been defeated, and will disappear completely after Groudon has been either caught or defeated.
Its counterpart is Marine Cave, and neither appears at the same time. The player must defeat, catch, or not visit one Legendary Pokémon before the other cave will appear.