This must be built on the coast. It lets you build small trading ships and small warships.
Layout environment, Dawn Pu on ArtStation at https://www.artstation.com/artwork/layout-environment
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Basic Dungeon Set
Under Siege: Modular Dungeon Terrain
Ye Olde Inn's Community Blog on HeroQuest: Inked Adventures review and contest!
modular dungeon section - Google Search
Advanced Gothic Dungeon Pieces Page 5