Sideways Cave

Sideways Cave is located just across the water southeast of the Imperial City's northeast sewer exit. The first level of the cave is inhabited by Daedra. In the northwest corner there is a secret door and it opens to reveal an Ayleid. The next part of the cave is a flooded Ayleid ruin with all sorts of floatsam strewn about. On top of a slab farther into the cave a tablet bears a rough translation of "Meridia-child, Earth root power, sea wave like. People out." There are three such tablets. The second tablet says "Fourth Star Hour Terror-of-the-most Meridia come". The third tablet says "Stone-Settlers not rest Meridia. Terror of the most Terror. Haste to safehome."

History
If you have read all of the tablets here is the story that falls into place.

Long ago, Ayleid settlers stumbled onto this grotto. They built a city here. While building the city, they uncovered a forgotten shrine to the Daedric Lord Meridia. Meridia's vengenace for this desacration was swift. She crushed the Ayleid city with her stone roots and buried the grotto almost entirely.