It’s getting cold outside and I don’t know about you, but I absolutely love pho in the winter. Your best bet for warm Vietnamese soon is Pho 75 in Arlington. It’s a no thrill, cafeteria style restaurant where the main and pretty much only attraction, pho, is offered in almost 20 different versions. The dining room is nothing special, just rows of tables in the Colonial Village, a strip mall looking row of restaurants between Rosslyn and Courthouse. But the pho is great and cheap (a large bowl will set you back less than $ 10) while the service is fast and efficient.
There are multiple other locations of Pho 75 in Northern Virginia and Maryland (Hyattsville, Falls Church etc.) but the one in Rosslyn is the only one that’s metro accessible.
Note: Cash only! (there’s an ATM inside though.)