Post Offices in Prague
To send a letter or a post card you can buy the stamps at the post office, some shops, tobacconists and newsstands. To send it afterwards just look for a orange post boxes they can be found without difficulty in the downtown area.
The Main Post Office - Praha 1, Jindrisska 14, open nonstop except break 12 p.m. - 02 a.m.
Local post offices are usually open 8 a.m. - 6 p.m.
The Czech Post - www.cpost.cz