how to trace network usage behaviour for particular user?

Good evening,

There's a need to trace visited sites for particular user in network due to suspicion of browsing social sites and playing games during working hours. These may be web-based or installed rpg games. Is there an efficient way how to collect statistics of such network usage?

I've found real time firewall logging feature but during fief hours of work there is an awful number of requests collected and its near to impossible understanding users networking behavior this way..

Any advice is highly appreciated.
Thank you!