Go through the circled wall. No one will ever see you there! :)
Grab these jumpboots and proceed to the picture below.
Either deselect your boots and go up lift and jump on the rail and try to jump to the ceiling or follow the arrows using 3 jumps.
Swim through the circled hole. Unfortunately this is the only "Finished" secret area in the RTNP DM maps to my knowledge. The one below looks like it was meant to be a secret area but was cut out?