Dome Rooftop Bar is a rooftop bar with beautiful views of Avenida de Mayo below.
This bar is opened seasonally in the summer months on the roof of the Tango de Mayo Hotel. The food is good, not great, but the view is excellent.
If you're looking for a hotel downtown, I highly recommend the boutique hotel Tango de Mayo. Avenida de Mayo is much more beautiful than busy 9 de Julio nearby with its chain hotels. Staying downtown is ideal for short stays of a day or two when you need to be in the heart of the action to see it all easily.