Hi there, One thing to watch out when using multiple terrains would be to use a reasonable detail distance. GPUI allows you to increase the draw distance a lot more than the Unity terrain, but if you have extreme max view distances, it would mean that GPUI will draw the details on other terrains as well. Also, when there are multiple terrains, the Tree and Detail managers are duplicated for each terrain. This results in more draw calls and so it would be better not to use very small chunks with GPUI. As for the spikes you mentioned, we have investigated this issue, and it looks like this issue is not related to GPUI. Apparently, the issue is caused when you don't have generated light map data in your scene whether GPUI is enabled or not.