The Stonestalker tribe of Beastmen in Stone Down can give you access to Howling Rock. However, getting their leader Hundred-Blood to agree to it will be difficult.
Travel to Stone Down Gorge. Wipe out the Scarlet Chorus you come across. Head west and down the walkways to reach Octave. Kill him. Go east and kill s'more.
Go south to run into Beasts. Now, you can attack (with Athletics 59 you can also scare them to get an edge in combat), insult, or talk to them that you come in peace.
Find Hundred-Blood to the north-east. Talk to her. Beyond questioning her on the traditions of her tribe, she's of not much use, as she will refuse to aid you. You can use Athletics 45 to instantly fight her or ask her why not, allowing you to either do a errand for her or fight her for the right of passage.
You can join the combat on either side, killing either Tangled Limb and the Chorus or Caedis and his Disfavored. However, note that wiping out the Chorus will not meet Hundred-Blood's demands... But killing Caedis puts Radix on a war path and you'll be forced to kill him later. Well, Isadora can always step in as the new leader...
You can assert your authority as Tunon's Fatebinder, explaining with Lore 26 that you are empowered to do so or intimidating them through force of arms. They will both start arguing who you should side with.
Ultimately, you can demand an inventive from either of them. Caedis offers his sword, Limb 10 , and Killsy suggests slaughtering them all.