Veloren worlds contain various kinds of sites for players to explore, some of which are more developed than others. The kinds of sites labelled on the map are described here along sites that aren't shown on map.
Similar to giant trees, large, walled castles are currently in Veloren and are present in the world as sites for RtSim NPCs to travel to, but have yet to serve a proper purpose.
Although giant trees are are generated at various locations across the world, they have yet to serve much of a non-aesthetic purpose. According to DevBlog#106, we hope is that they will become sites containing villagers or small towns.