The Glowing Sea

The Glowing Sea is a main quest in Fallout 4.

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

Travel to the Edge of the Glowing Sea and head southwest, following the remains of the freeway until the Pip-Boy indicates a hike off-road is in order. Expect to face Deathclaws, radscorpions, feral ghouls and other irradiated wildlife. Upon reaching the map marker, the Sole Survivor will find themselves close to the Crater of Atom, a site holy to the Children of Atom.

Upon entering the location, the Children's leader, Mother Isolde, will inform the Sole Survivor that they are trespassing. Though violence is always an option (search the area for a scrap of paper indicating a nearby cave), it is possible to lower one's weapon and speak to Mother Isolde instead. Answer her questions politely, and she will give directions to a rocky cave nearby.

Locate the rocky cave roughly southwest of the Crater of Atom, being wary of the roaming deathclaw in the area. Virgil will be found inside this cave. He requests that the Sole Survivor help him locate a serum within the Institute, in return for his knowledge.

Bugs

 * Upon entering the cave, Virgil is not there. The marker for finding him points to the ground. This may be the result of having visited Virgil's cave prior to the quest.
 * On PC, using console command and then  may force Virgil to appear in the cave.