Ocean Monument has no inside, is just a shell of one filled with water and gaurdians.

Two Ocean Monuments I found in my MCPE world on easy had absolutely NO inside structures like computer, only were just a shell of one filled with water and guardians. No Elder Guardians either, so no sponge and I missed out on two Xbox live achievements.

seed: 2064198885

go to 647 100 -1717 on EASY difficulty

also 186 100 -1833
-you may need some searching because those are not exact coords.