A helix made of stairs going up to a sky-base [base in the sky, not /warp skybase], I made a helix once, it looks really cool.
Massive desert biomes with temples etc and villages plus grasslands with acacia trees and tall mountains and lagoons next to mushroom forests and maybe a mushroom biome add waterfalls as well
I made one of those on a different server with like a house and cave and lava pools and everything it looks so cool but it took forever