Ultramarine Stronghold

Ultramarine Stronghold - is an area in B3313.

Description
As player might guess from the name, this is a solid stronghold, surrounded by water and mines and guarded by Goombas, Bob-ombs, Chuckyas, and Motos. Beneath the fortress is a network of water tunnels, also filled with mines. There are grates in the tunnels, but they don't lead to anything of note, so the Vanish Cap is not required to complete this level.

Origins
It appears to be an original creation.

The music is the underwater theme from Super Mario Bros played in the Super Mario 64 sound font.

Stars

 * Collect 8 red coins.
 * Collect the star at the top of the stronghold.

Leading here

 * 4th Floor: Enter the upper left door, then jump into the painting.