I am not sure if this has been stated anywhere in-game or by the devs, but if you take a good look at Jorrvaskr from the outside, the roof is a ship. Considering, Ysgramor was the first Atmoran on Tamriel and he founded the Conpanions, I think it's safe to assume that ship is what they sailed in on. One could say that the roof of Jorrvaskr is the oldest man-made (discounting Mer) construction in Tamriel.

What other little lore-based features or Easter-eggs have y'all noticed?