Eildon's Ward.
On my way back to Urshilaku, I came across a dungeon. I recognised the name from somewhere as a Daedric ruin, but I wasn't sure from where, and it didn't look much like a Daedric ruin. Inside I killed a couple of people and their scamps, and read a notice talking about great treasure. "Cool!" I thought, and went further into the more Daedric-ey cave.
I had to kill a few dremoras and go through a maze to get there, but eventually I found a door. I opened it with my skeleton key, and a golden saint ran out and I fought her, winning. Then I went inside the room. It had skulls with daggers in on the left and right, but I didn't need them. At the far end there was a corpse, and it had a Daedric Shield.
"SCORE!" I thought, picking it up. I was over-encumbered, so I dropped the Saint's shield I had been holding. Then I opened a couple of chests so get a fair bit of cash. Then I turned around and left the room.
When I got out of the door, I stopped, and turned around. I'm not exactly sure why - maybe it was to take it all in, maybe it was just to close the door. But when I turned, I noticed that above the corpse was a glowing crest.
A couple of minutes later, I put down my daedric shield