grimwerk: The world of Arx was a pleasure to explore. Sadly, the last two levels were so buggy and incomplete that I couldn't enjoy the end. This was years ago. Hopefully, some fans have patched the game into something more satisfying!
You are right, the game was poorly optimized back when it first came out but fortunately a group of talented people has developed a completely new engine for the game and they are still improving it, it is called
Arx Libertatis if you didn't already know about it.
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Here is my new masterpiece, it should be pretty easy to guess this time.