Head down the steps and enter the building through the red door at the end.
Luckily, there's a store in Diamond City that can help - so open your map, fast travel back to Diamond City Market, then locate Fallon's, directly west of the Power Noodles bar. You've already acquired a reasonable selection of meds from Doctor Amari's office so, next, you'll need to find a decent hazmat suit. Before you set off on your travels, however, you'll need to ensure that you're suitably prepared for the radioactive perils that await you. The Glowing Sea lies a fair distance to the south-west of your current position, so you've got a long journey ahead of you. When you're done, exit the Memory Den and return to the street.
Once Nick gets to his feet, he'll ask if you're okay - wrap up the conversation then prepare to leave. Finally, decide if you want Nick's company as you search for Virgil - we'll be taking him with us, so consider doing the same. You'll notice a change in his tone - so ask about Kellogg and see if he has any ideas about tackling the Glowing Sea. Join Valentine by the doorway to the north and engage him in conversation.