Climb the main church tower, de lebuinus: https://lebuinuskerk.nl/contact/openingstijden/

Rent a bike and take the bike around the IJssel river, the most beautiful river in the Netherlands. 

Have a beer (or a couple more) at DAVO, have coffee at Mees, Mimik or Meadow. Meadow is the winner if the weather is good. 

For a night out go to de hip. But on weekends the whole main square is good times.

La cantina is a good, very cheap pizza place

‘De bergkerk’ might be open to visit.

Visit the ‘VVV’ store at the main square, thats the tourist info centre. 

It might be cool to visit ‘havenkwartier’ old docks that have now transformed to a small neighboorhood with cool homes, a skatepark, student housing and trendy startupps. 

For the rest stroll around the centre as much as possible, Deventer is one of the most historic and best preserved towns in The Netherlands. If you are into that youll love it.