Terra Cave

Terra Cave, Hoenn (from Pokemon Emerald).

How to get here. Only after the Hoenn Hall of Fame. Talk to the scientist on the second floor of the Weather Institute on Route 119, or to the sailor in the Slateport harbor: they name a route where abnormal weather has started, and it lasts about 1000 steps. Terra Cave (Groudon, level 70) shows up in drought on Route 114, 115, 116 or 118. Once one of the two is beaten or caught, only the other comes up.