B21 Cocktail Bar runs out of a single narrow room on the ground floor of Hotel Allure at Bílkova 854/21, a few steps north of Old Town Square, and it leans into the constraint: this is one of the smallest cocktail bars in Prague and it makes the tight footprint part of the appeal.
The concept is the draw. The B21 list carries fourteen signature cocktails, each tied to a different region of the Czech Republic, so the menu reads as a short tour of the country rather than a greatest-hits sheet of international classics. According to the bar's own site, the drinks are built to "travel across the Czech Republic, one glass at a time," and the bartenders treat that brief seriously, working Czech spirits, herbs, and fruit into the builds.
The room itself seats only a handful of people. Dark walls, low light, and a compact back bar set the tone, and the close quarters push guests toward conversation with the bartenders rather than each other. Tripadvisor reviewers return again and again to the same two points: the staff explain every drink, and the small footprint fills fast once the after-dinner crowd arrives.
What to order
Order straight off the regional menu rather than asking for an off-list classic; the fourteen house drinks are the entire point of the visit. Cocktails sit around the 250–350 CZK mark, in line with Old Town cocktail pricing. Tell the bartender which Czech region sounds interesting and let them steer, since the menu rotates and each build is designed to read as a place rather than a flavour.
Who it's for
B21 suits drinkers who want a guided, sit-down cocktail hour and a reason to talk to the person mixing the drink. It is a poor fit for big groups or anyone after a loud night out, because the room cannot hold a crowd and the experience depends on the bartender having time to talk through the list.
Best time to go
Arrive on the early side, soon after the 2pm open or in the first hour after dinner, to land one of the few seats before the room fills. Late evening on a weekend means standing or waiting. For wider context, see how it compares on our best cocktail bars in Prague list and across the rest of the Prague bar guide.
