Are you in Euryale heading for the Golden Fleece?

First, you must pull the right lever to lower the bars to a dead man's alcove. Once in there, attack the breakable wall to reveal a stream of water. Kill the Undead that appear and then pick up the dead body and drop it into the stream. It will float away out of sight.

Next go over to the switch in the left alcove and break through the wall behind it. There you'll find that same stream of water you dropped the dead body into.

When the body floats by, grab it and put it on the alcove switch. Then, you can stand on the main switch and lower the gate in front of you to escape.