Take the Zerzala portal into Steppes and head over to the entrance of the Arcanum Conservatory at /setwaypoint 15434 7187
Go down into the tunnel, find the junction and turn left. This will take you into a tunnel that is filled with water. You need to follow this tunnel all the way down.. its very long! (as long as you keep swimming you shouldn’t need any underwater breathing pot for this, the tunnel isn’t long enough for you to die).
While you are down here you may want to collect the soap needed for the Ardent Domain Puzzle.