The entry condition
Jagex’s Fellhollow update gives a specific prerequisite: finish Dragon Slayer, then talk to the Wise Old Man. The region lies north of Ghornfell. If the route is not available, check that the quest is complete and return to the Wise Old Man before assuming that the map is broken. The official note does not provide an exact coordinate or a step-by-step path from every possible base, so neither does this guide.
What changes in Fellhollow
Fellhollow added new enemies, vaults, quests and two named NPCs: Death and Postie Pete. Death’s Shop allows resource exchanges for rewards. The update also introduced the Withering status effect; cleansing pools in the region can remove its effect. These facts help you plan what to carry, but the official announcement does not give a complete enemy route or a safe path through every vault.
The area brought a new material tier and the Castle building kit. Jagex names Steel Armour, Green Dragonhide and Splitbark armour in the same update. This is a useful milestone for equipment planning, though it is not a claim that one set is universally best.
Other systems introduced with 0.10
The Fellhollow release also added Farming and Terrorbird mounts. Farming brought new plots, water and compost stations, and the tools used with them. A Terrorbird can be summoned and ridden in the overworld. These features appeared with the same update; the announcement does not establish that they must all be unlocked immediately upon entering Fellhollow.
For the wider release sequence, see Ashenfall Regions. Bring gear suited to the area, follow the in-game quest markers and treat the game’s current prompts as more precise than an old screenshot.