Explicitly Rewarding Discovery

Here's what it looks like when you discover something interesting in Lone Spelunker:

If there is a "score" in your game, it's the number of "discoveries" you've made in the current cave.  In addition to the normal cave geography, which is fun to explore on its own, little "troves" of discoveries are added in places where they logically might appear.

In addition, to support some real-world interest in caves, cave ecosystems, and the sport of spelunking, many of the discoveries have a link to the corresponding Wikipedia page on the subject.  Not only does this support the educational aspect of the game, it also (hopefully) will help break down the "ASCII view" of the game for people's imaginations and help them see in their mind's eye what the game is trying to model.  And more to the point, perhaps reading the Wikipedia page and learning something new about real-world caves you didn't know before might help add to the sense of discovery.  Caves are surprising and bizarre ecosystems, and most people know very little about them.  This connection with real-world caves makes the discoveries you make grounded in reality, which makes the simulation feel all the more real.