The building is a small cellar. It has a set of stairs on the eastern side leading to a small platform above where a Join the Railroad holotape can be found. The cellar features several closets and mannequins. The store sells an assortment of pre-War clothing, as well as more useful items such as bobby pins and hazmat suits. If the building is locked, simply wait until Becky Fallon (the owner) who can be found near the noodle stand to get in her store (sometime after 8 A.M.)
Fallon's Basement appears only in Fallout 4.
Behind the scenes
"Fallon's Basement" continues the pun on the well-known real life New England department store chain Filene's, whose discount locations (originally located in a sub-level of the flagship Downtown Crossing store) were branded as Filene's Basement.