Spoiler: tip Bring some Potions of Wolf Speed, these last 10 minutes, which should be more than enough if you make no big mistakes. Combining with Dash or Sprint will help too. Having Silent Movement is highly recommended.

Spoiler Use a Potion of Wolf Speed, then run through the first and second open gates before they close. Rest a moment, cast Silent Movement, and make your way to the next doors. Kick them open. If the first gate is closed, do not go in. You may want to switch to private mode, because that means someone else is in the area and could mess you up.

Spoiler Now you have to cross the poison pond. If you can make it on the logs alone, great. If you fall, run to the land areas on the right, and then heal like crazy. You can safely reach the end from the farther land area.

Spoiler Now proceed to the next open gates, then run through them and the next open gates. Dash alone is enough to make it through.

Spoiler Re-cast Silent Movement, then make your way around, first to the right, then in front of the second wall, then up on to the left corner of the far wall.

Spoiler Re-cast Silent Movement again and follow the far left wall to the far left corner.

Spoiler Go through the trap door in the floor of the corner tower, you should see a skeleton glowing blue. Search the skeleton and you will find...

Spoiler ...just a shard of the lens, plus a note about how it got broken