Control Resonant: All Astral Key Locations in The Underpass Resonant

The Underpass Resonant is a side quest that drops a long Astral Plane platforming stretch between Dylan and the region’s boss. It begins at a spire made of Astral material standing right next to the Fast Travel Door in Underpass 4, inside Downtown. Once you enter the spire, you land in a fractured white void where three Astral Keys open three consecutive locked doors before the boss arena.

Quick answer: You need three Astral Keys, and none appear on your minimap. Stand with your back to each locked door, follow the path it points you toward, grab the key, and return. Each door reveals another locked door behind it.

Reach the Astral Plane spire in Underpass 4

Use Fast Travel to reach the Spire travel point if it is unlocked; if it is not, let the quest marker lead you over shifting platforms and warped terrain until you reach the structure.

Underpass map location — The Underpass 4 map with the highlighted Fast Travel Door. Shown at 00:05 in 100% Guides’s video. Image: Remedy Entertainment

Climb the concrete wall platforms up to the spire and clear the enemies guarding the entrance. Pass through the gap and step into the white portal to enter the Astral Plane. From here, the Shift ability is essential, since much of the route requires moving between surfaces that face different directions.

Crossing high floating pillars — Air-dashing across the high floating pillars inside the Astral Plane. Shown at 01:00 in 100% Guides’s video. Image: Remedy Entertainment

Cross the floating monolithic blocks by jumping and air-dashing, then head to the main column and run to its end. There you find the first set of double doors, which are locked. Interact with them to confirm you need a key, then leave to search the surrounding paths.

Dropping through vertical passages — Dropping down through the vertical passages between Astral walls. Shown at 01:29 in 100% Guides’s video. Image: Remedy Entertainment

All three Astral Key locations

Each key sits inside a glass box at the end of a branching route. The doors chain together, so you will unlock one only to find the next barrier directly behind it.

First Astral Key

With the first locked door behind you, take the route on the right. Enemies in this section are tougher and more durable, so defeat them before moving forward.

Move through the traps where spikes shoot up from the ground. At the second box that activates a spike trap, turn right and follow the straight path to its end, where the first key awaits.

First Astral Key obtained — The first Astral Key rests on a desk at the end of the right-hand path. Shown at 01:35 in 100% Guides’s video. Image: Remedy Entertainment

Go back the way you came and unlock the door with the key. Beyond it, you will find only a second locked door.

Second Astral Key

Turn away from the second door and run straight to the far end of the path. Jump the gap and fight through the enemy group waiting on the other side.

Outer ring platforming — Working around the outer ring of monolithic structures toward the second key. Shown at 02:30 in 100% Guides’s video. Image: Remedy Entertainment

Push through the next spike section and the following enemy encounter. Keep climbing until you reach an area with a chair and a TV.

Beside the chair and TV, press Shift twice to drop down. Jump to the opposite side and take the second key, then return to unlock the door and reveal the third locked door.

Third Astral Key

With your back to the third door, move forward until platforms appear on your left. Ignore the first one and float across to the second platform instead.

Navigating fractured blocks — Leaping across disconnected columns on the way to the final key. Shown at 02:33 in 100% Guides’s video. Image: Remedy Entertainment

Chase the box that keeps teleporting away as you approach. It eventually spawns enemies, so clear them before moving on.

Continue along the path to pick up a Health Upgrade, then reach the third key in its glass box. Grab the nearby chests and resources before heading back.

Unlock the final door and start the boss fight

Take the third key to the final locked door and interact with it. No additional keys can be found after this point. Proceed along the hallway toward the glowing white figure to start a cutscene. The objective changes to Kill the Astral Plane Resonant, and you enter the open arena for the boss fight against The Physicist.

The quest is confirmed complete once you defeat the Resonant. You are then given a choice between the Spike and Astral Rebuke combat abilities, and you also receive the Untapped Golden Earrings Artifact Recipe.

Because the keys never appear on the minimap, always return to the exact locked door and face away from it before starting each search. That orientation is what keeps the branching routes readable in the shifting Astral Plane.