Usually really big mountain biomes have a spawner somewhere around the top.

The first bosses we found really easy. But the Mountain boss was the first one that took us awhile, I think we went through 4 or 5 whole mountain areas before we found where the boss was. So far same thing for the Plains boss to (we have checked about 7). First 3 bosses we found pretty easy but these last two took awhile lol. Just check every area of the mountain biomes and you should find it at some point, its different for each seed/world where they are located on the map. Good luck!

Big map, i have hit up 3 smaller mountains nothing a buddy found a stone telling him where to go on a bigger mountain at the top

you will probably need to visit a lot of mountain biomes and find those rock towers. Inside will have the boss special rune with its location

mountain most at the top..
http://valheim-map.world/ only use this after 100h searching :)

Look for fortresses near mountain summits. Inside you will often find a stone that will reveal the nearest spawn point.

Originally posted by Elidrin:

Look for fortresses near mountain summits. Inside you will often find a stone that will reveal the nearest spawn point.

Yeh ok. I am not finding many but I think I get it.

Originally posted by Cockroach:

Originally posted by Elidrin:

Look for fortresses near mountain summits. Inside you will often find a stone that will reveal the nearest spawn point.

Yeh ok. I am not finding many but I think I get it.

Some maps are bugged. I think they fixed this in the patch before last, but if you created this map before then, it could be one of the bugged ones. The bugged ones have no moder at all. See the patch notes for details, there is a way to fix this.

You can tell if you map is bugged by putting the seed into this website and then selecting to show either the Boss Stones or Bosses:
http://valheim-map.world/

Some maps were bugged so yours might not have it. Maybe I am mistaken but I remember seeing in patch notes something along the lines of being able to use dev commands to generate an alter correctly. No idea how that works since I haven't had to do so. But of course if that is actually a thing be careful with commands.

Originally posted by Cockroach:

I cant find anything that will show where Moder is..
Where can I find this ??
I am wandering the mountains but nothing about,.

You find it like you do all other bosses.

Originally posted by Cockroach:

I cant find anything that will show where Moder is..
Where can I find this ??
I am wandering the mountains but nothing about,.

If you've already beat the Bonemass, you can find the map marker stone behind the skull altar.

Originally posted by OnlyZuul:

Originally posted by Cockroach:

I cant find anything that will show where Moder is..
Where can I find this ??
I am wandering the mountains but nothing about,.

You find it like you do all other bosses.

Well, kinda. But not really. 3 SP and 2 MP playtroughs and i have seen only one rune stone for moder. Usually found the spawn point itself after exploring a lot of mountains. Same for Yagluth.

Originally posted by SiEgE:

Originally posted by Cockroach:

I cant find anything that will show where Moder is..
Where can I find this ??
I am wandering the mountains but nothing about,.

If you've already beat the Bonemass, you can find the map marker stone behind the skull altar.

I tried that but it said I had already found it

Originally posted by SiEgE:

Originally posted by Cockroach:

I cant find anything that will show where Moder is..
Where can I find this ??
I am wandering the mountains but nothing about,.

If you've already beat the Bonemass, you can find the map marker stone behind the skull altar.

I check my map again and moder was already there.. LOL .
This is correct then

If it incourages you there seems to more than one of them alters for all 4 boss's, I found 3 Elders register stones and 3 Elder alters. Same with Bonemass 2 of them.
Also 2 of the others.
For Modor I found his register inside of one of the towers in the mountain. His first alter I that was shown on the map is also in the highest mountain.
One of these stone towers
https://steamcommunity.com/sharedfiles/filedetails/?id=2431129597