It might really be the case, when the plane or a bus arrive late at night to Riga airport or to the bus station and there is a real need for some night food in town. Where to get a proper sandwich? How not to get lost on long streets of Riga? To be honest, there are not that many restaurants and bars, which work late at night. Here are just the two of them, where it is possible to get some food for sure.
One is the sushi bar in Casino Olympic (http://www.olympic-casino.lv/ca…/olympic-voodoo-casino_n120…), which is open 24/7.
The second one is Delisnack Fontaine, where tasty burgers are made. It does not work 24/7, but it is open quite late after the midnight. They have the working hours on their web page http://www.delisnackriga.lv/en/page/contact.