Seafloor Porthole - Large

 is a rare base item.

Obtained from

 * Atlantean Quartermaster
 * Mutineer Quartermaster

Feats

 * Superhero Staycation: Collect all 20 Base Items from the 2018 Tides of War seasonal event

Trivia
The item is only available from seasonal vendors during the Tides of War summer event.