I have had a bonemass surrounded by plains and an unscalable mountain.
https://steamcommunity.com/sharedfiles/filedetails/?id=2860824938
You'll need the onion seeds and the wolf meat from the mountains. You can sneak slowly through the plains. You have to watch out for deathsquitos and shoot them from range with your bow. You have to watch for an avoid Lox but they have short perception ranges and its easy to sneak past them without alerting them. That leaves listening. If you hear squishing but don't see any growths or tar pits they are behind the rise that you can't see over. Give that rise a wide berth and listen for the giggling of the fulings. If you hear that you'll need to skirt that area too.

Golems are OK. You can handle them if you are careful. You need an iron mace as golems have no weaknesses and are resistant to many damage types (like piercing from arrows). There are 2 types of golem one is right handed the other is left handed. Dodge until you can figure out which hand the golem uses and then dodge toward that hand on subsequent attacks. If you can get to his side you can get in 2 good swings before he can turn around.

The other reason golems are good is because they spawn near abandoned buildings or silver veins and chests in the abandoned buildings are where you'll can find onion seeds (they are rare though my first play through it took me 6 abandoned buildings to find my first onions seeds.) If you see a golem and there is no building there is a silver vein nearby. You can try digging around trying to find it without a wish bone but sometimes you can see part of a silver vein protruding from the terrain if the peaks are especially sharp.
https://steamcommunity.com/sharedfiles/filedetails/?id=2931149861
Something like that can provide you with enough silver to build a silver shield. With a silver shield you can stand up to a fuling as long as you are one on one with them which makes sneaking through the plains to get to bonemass easier.