Many fine private art galleries showing contemporary work by Czech and other artists are in central Prague, within walking distance of Staromestské námestí. Although their primary interest is sales, most welcome browsing.
As for public museums and galleries, note that many museums are closed on Monday.
National Gellery Sites--The national collection of fine art is grouped for display in the series of venues known collectively as the National Gallery (Národní Galerie). Remember that this term refers to several locations, not just one gallery.
The most extensive collection of classic European works spanning the 14th to the 18th centuries is found at the Archbishop's Palace complex in the Sternberský palác across from the main gate to Prague Castle.
Veletrzní Palace houses most of the country's 20th-century art collection and now also shows the important national revival works from Czech artists of the 19th century. Much of the rest of the national collection is divided between Kinský Palace on Old Town Square and the Gothic collection at St. Agnes Convent near the river in Old Town.