Sunken City

Sunken City is a location searchable by Toothless in the game, Dragons: Rise of Berk.

Geography
This oddly named island doesn't appear to have human structures on it, based on its image on Hiccup's Race to the Edge map. It looks rather barren, perhaps muddy (solely based on the darker brown shade) with a lake and either a mountain or a pit at its center.

Other Appearances
Sunken City does appear on the Interactive Map on the Dragons: Race To the Edge website. The island thus far is not featured in this TV series, however.