There are seven drainage chambers and two sealed cisterns scattered around the Capital Wasteland. These are minor dungeons, and all are home to Fallout 3 radio stations broadcasting Morse code (except Oscar Zulu and Yankee Bravo). The particular message is explained at length on the page for signal Kilo Bravo. Many of the stations do not have a map marker, but can be spotted easily from far away by looking for the tower.