how to get back to starting base

first thing you should do is play the game until you get the building tool, but it is important that you restart the game at least once in your playthrough

you need at least 2 lead and 2 titanium in your inventory for this to work

now that you're ready to go to the starting base, go to the place you first see the penglings when you get out of the ice caves. go along the wall and find the hole, go through it.

once you get to the open spot with the radio tower, simply build a foundation along the wall of snow next to the radio tower, it is important that you build in the place shown in this image because otherwise you cant climb it.

this is the trickiest part, you need to get on the foundation and jump against the snow with your camera pointed upwards keep jumping with sometimes going left or right, it may take some time but eventually you will get on top

you can save the game or do whatever you want, its a good spot to check out the new hoverbike, there's already a guide how to get it so check that out if you want to.