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Route 108 has a large, abandoned ship midway. You'll have to battle some trainers to get to it.

• Swimmer Tara
  • Horsea (lvl. 26)
  • Marill (lvl. 26)
• Swimmer Jerome
  • Tentacool (lvl. 26)
  • Wingull (lvl. 26)
• Swimmer Missy
  • Goldeen (lvl. 24)
  • Wingull (lvl. 24)
  • Marill (lvl. 24)
  • Wailmer (lvl. 24)

Go north to find the Abandoned Ship.