Seaside Cave

The Seaside Cave is a cavern located between Route 21 and Undella Bay. It is accessible as soon as the player gets to Undella Town; however, Black Belt Rocky blocks the player from exploring the cave until they push Team Plasma out of Opelucid City. It is also the first area in the game where an HM is needed to proceed, as Surf is required to reach Seaside Cave via Route 21 or Undella Bay.