GW2 Forgotten Stream achievement guide with detailed walkthrough. Forgotten Stream is a new achievement added with the Halloween patch and it is located in Cursed Shores.
Behind the Cathedral of Verdance is a is a river and there is a semi hidden path you can go through, The door at the end of the path is locked there are plenty of fast respawning risen along the way. Bring a friend if you don’t feel confident soloing all the risens. No chest here but you will get the Forgotten Stream achievement near the locked door.