Horse Skull is one of the 50 Mongol Artifacts, pieces of the invaders' culture and warfare you can study. It sits at Mountainside Ruins in Toyotama, and finding 20 artifacts counts toward the Know Your Enemy trophy.
Head to Mountainside Ruins in Toyotama and search the area for the item. Mountainside Ruins is a Mongol-held territory, so expect to fight or sneak past guards before you can search it.
Akashima Bamboo Strike
The Akashima Bamboo Strike is a sword-timing challenge near Fort Ito in Toyotama. Cut through all the bamboo with the right buttons and it counts toward raising your maximum Resolve.
Akashima Haiku
The Akashima Haiku is a poem spot where the river meets the sea, just south of Old Kanazawa Marsh in Toyotama. Sit down, pick three lines and you earn the Headband of Uncertainty.
Akashima Lighthouse
Akashima Lighthouse is one of the 10 lighthouses Jin can relight, at Fort Ito, Toyotama. Lighting the fire gives a minor boost to your Legend.
Amber Assassin
Amber Assassin is a dye for Ronin Attire. It costs 10 flowers at the Toyotama merchants. Like every dye it only changes colours.