There are a lot of abstract strategy games in the Looney Pyramid catalog. A good chunk of the early games, for instance most of the games in Playing with Pyramids, are pure abstract strategy games without any random elements.
Played out on a five by five grid, Volcano is a game about collecting sets of pyramids by strategically causing volcano eruptions. Some years ago, I wrote a fairly detailed review and rules summary : https://www.boardgamegeek.com/thread/202091/very-unconventional-abstract Looking back at it, I have to say that Volcano is much easier to demonstrate than to explain.
The thumbnail sketch of Volcano is that you move the volcano caps around to cause eruptions, which are basically the pyramids playing hopscotch. When a pyramid lands on another pyramid the same size, you get to keep that pyramid for scoring. You get extra points collecting a trio of the same color and when someone gets a pyramid in every color, the game ends.
There is definitely a learning curve to Volcano. As I said, actually understanding how the game works mechanically doesn't seem to click until you see the game in action. The next part of the learning curve is figuring out how to set up good moves :D
Volcano is a game that really requires the stacking nature of the pyramids, as well as three different sizes. It clearly was developed out of the very nature of the pyramids. Plus, there's no denying that, as abstract as it is, the pyramids help it live up to the Volcano name.
Plus, Volcano is a very solid game. Definitely forces you to think in different ways so it is intellectually challenging. At the same time, causing eruptions and collecting colorful pyramids is an off a lot of fun. For such a different game, it's an easy one to get people interested.
I've been playing Volcano for years. Sadly, not regularly enough to get really good at it but I keep coming back to it. I consider it one of the games that really elevated the Looney Pyramid system, a game I'd buy and keep playing even if it was the only game in the system.