Rock Creek Caverns

If you explore the extreme North past MDPL-21 Power Station, you'll see three adventurers being attacked by a Deathclaw. If you save them, one of them will give you the location to Rock Creek Caverns. You may also encounter this group in the Temple of the Union after the slaves have departed.(This is a random Encounter, and can happen any number of places)

The Rock Creek Caverns are located in the east/southeast portion of the Capital Wasteland. It is located west of the National Guard Depot.

The Caverns are accessed through a sewer grate at the bottom of a radioactive-water filled crater that has exposed the sewer system. The sewer network is attached to a short segment of subway system, which then descends into a cavern system filled with Mirelurk, Mirelurk Hunter, and Mirelurk King creatures. There is lots of water - a Radiation Suit or Advanced Radiation Suit will come in handy. At the end of the cavern system, there are a number of dead adventurers and an ammunitions cache, with at least one Laser Rifle and associated ammunition.