They can make ice bridges.

So first you have to toggle skills to the ice bridge, and then activate it and build as you would build a structure. Take caution, as when you build a bridge the old one disappears. This could also be useful to defend from rival players, as you could run up a bridge and make a new one so the old one disappears, rendering the enemies’ melee useless. The bridge ability also has a short cooldown. Also, you will never fall whilst building a bridge because the base is always under you. You can walk off a bridge AFTER building it, though, so be careful.

-TheFlamingFeatherlight