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.

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.