A bus will drop you off at work; read the wall to see the movement controls for your chosen input device. Head north, through the metal detector and up a few flights of stairs, and find Chandler the Handler. A cinematic will play, and you’ll learn you’ve got a Giant Soul to snag, and that you’ll be mortal as long as the door to that soul is open.
If you want to earn the Academy of Umbrellas achievement, you’ll need to get and equip the Umbrella before you engage in any combat. It’s nearby, up the stairs to the west after you speak with Chandler — the Umbrella is leaning against a lamp post.
Head up the elevator to the right of Chandler’s desk, and then go north-west to the door.
Once you’re through the door, there’s really only one path you can take. Follow the directions that appear on the walls to learn the rest of the controls. Hit the first glowing pink cube with your sword to open the gate.
Then head back the way you came and through the now-open gate, then up the next set of stairs. Use your bow to hit the cube on the pedestal, then head through the nearby and now-open gate.
Hit the cube by the closed gate that leads back to the door you first came here through — this will be helpful if you end up dying to the boss. Then go north-east to confront your first enemy in Death’s Door: The Demonic Forest Spirit.
How to Beat the Demonic Forest Spirit
You can sneak a few hits in as soon as the fight starts, so do that immediately. Then run counter-clockwise the same direction the boss’ arms are rotating, staying between the arms.
After the arms drop, hit the Forest Spirit twice with your sword, then continue running counter-clockwise. If the Spirit wraps their arms around their body, run as far away as possible. It will spin and move towards you; stay out of it’s way, and use your bow to deal some damage when it is safe to do so.
Once you’ve done enough damage, the Forest Spirit will raise up on two legs. Attack one leg until it no longer flashes when you hit it, then run to the other one and do the same. It will settle down again and attempt to attack you more, but a few more attacks should finish it off.
Congrats on your first victory in Death’s Door! Unfortunately, you’ll find that this job isn’t going to go smoothly. After the brief cinematic ends, head through the open door.
You can earn the “Conga Line” achievement now if you want, by slowly heading out of the boss arena southwest, and then leading the nearby flower spirits back towards the boss arena. They might not follow you inside, but as long as all the spirits are still attempting to follow you, you should earn the achievement. Credit for this tip goes to EIP user Ava Tarmona.