Not going to post any of the really cool things that I consider spoilers, but here are some other things I've noticed which no one has posted yet.

The names of the lightroots are the names of the shrines backwards.

Every little mine has one chest, usually containing 20 crystalized charges, but sometimes a unique item. They are easy to see on the map.

Big monster lairs are easy to spot on the map, too, once you get use to their appearance.

Groves of trees (the little starhshaped dark trees on the map) very often contain a giant hollow tree stump with a chest in it. You can learn to recognize these tree stumps on the map.

I had no idea that was the case with the groves! I'll have to go back through some and try to find the chests.

After pretty much fully exploring the Depths, I must have found 10 Old Maps where I already had the treasure. Thankfully, the game recognizes this and doesn't waste your time by placing an X on the map.

Huh, all the Old Maps I've found so far have led me to treasure chests in various mines. Had no idea they could lead anywhere else!