Some personal Belgrade favorites of the organizers:

Belgrade on Lonely planet:   https://www.lonelyplanet.com/serbia/belgrade
"Outspoken, adventurous, proud and audacious: Belgrade is by no means a 'pretty' capital, but its gritty exuberance makes it one of the most happening cities in Europe. While it hurtles towards a brighter future, its chaotic past unfolds before your eyes: socialist blocks are squeezed between art nouveau masterpieces, and remnants of the Habsburg legacy contrast with Ottoman relics." 

A cool blog about Belgrade lifestyle, full of hidden gems:   http://bellegrade.com/