The Glowing Sea

The Glowing Sea is a main story quest in Fallout 4.

Quick walkthrough

 * 1) Find Brian Virgil in the Glowing Sea.

Detailed walkthrough
Kellogg's memories and Doctor Amari's advice indicate one should locate an escaped Institute scientist, Virgil. His last known position was deep in the most irradiated region of the Commonwealth—the Glowing Sea.

Commence the long trek southwest, following the remains of the freeway until your Pip-Boy indicates a hike off-road is in order. Expect to face deathclaws, radscorpions, feral ghouls, and other irradiated wildlife. When reaching the map marker, the player character is close to the Crater of Atom.

When entering the location of a strange cult, led by Mother Isolde, the Sole Survivor is actually trespassing. Though violence is always an option (search the area of a scrap of paper indicating a nearby cave), one can lower the weapon and speak to Mother Isolde. Answer her politely. She directs to a nearby cave.

Locate the rocky cave roughly southwest of the Crater of the Atom. Watch for, or sneak past, the roaming deathclaw.

The Sole Survivor will find Virgil inside this cave. He requests to help him locate a serum within the Institute in return for his knowledge.

When entering Rocky Cave be sure not to destroy any of Virgil's defenses. Any defenses destroyed prior to returning to complete the quest will result in failing the quest when returning with the serum. Virgil will immediately turn hostile when you return.