An incomplete Ritual Site may hide a "Feaster" – if a Ritual Site reveals a feaster, power will be generated as normal, but the ritualist is not merely driven mad - they are actually devoured by the Feaster! In addition any sacrifices in water connected to that ritual site are also devoured and each sacrifice and ritualist devoured gains their Cult a lot of power, but a dead cultist can be hard to recover from unless you plan carefully!
I like games with what I call "strong crescendos". These are actually fairly easy to implement with the likes of simple dice rolls but can be double-edged swords. For example, Dead of Winter implements both good and bad examples in my opinion. Good: you roll your action dice in advance and can spend them as you will - so you have a turn like: "ooh! 2 fives and a six! I'm going to kill SO MANY ZOMBIES this turn!" Bad: one of your team goes out to the convenience store: "Oh, he's dead."
Its trickier to build crescendos without that strong random element, but if you can do it, its much more rewarding for your players to pull off. Ritual sites are a big source of crescendos in Carcosa. If you draw and place a ritual site that hides a feaster, you suddenly have a whole new set of goals, challenges and decisions to make:
Firstly it's a ritual site, so you want to surround it to complete it for maximum power generation, but if it's one of the ones that shares a tile with a ley line or district segment, your opponents will be trying to complete those features to cause it to trigger too early, denying you points.
Secondly, if you deploy your Ritualist they are going to die. Do you have the means to replace them or will you have to struggle on without them. An early game death, or one where you're already stretched thin, can cripple your chances of victory.
Finally, you now know where a Feaster is going to appear! Do you, in later turns start sacrificing cultists to connected waters of Lake Hali for greater power? Your opponents will be watching, will they then follow suit, or worse start trying to premeturely trigger the Site when they weren't before!
Carcosa, unlike other tile laying games, scores in "leaps" more than steps - and the ritual sites are the most obvious example. We've seen ritual sites score cults over 20 occult power in a single resolution and given that for the four player game, only 50 is required to start the final ritual - that can make a massive difference to the leaderboard!