The Kilianipark, located in Erfurt's northern district of Gispersleben, is where the annual parish fair and the May Fire are held. The park has many open meadows and is a lovely place to relax and stroll through. An added bonus is the children's adventure playground just to the south of the park.
The Kilianipark is some distance outside the city centre and can be reached by tram (no. 1 or 3 - Europaplatz final stop). From there, you can either walk to the park (10 minutes), or take a no. 10 bus from Europaplatz, descending at the Akazienallee stop.
Alternatively, why not combine your visit with a pleasant bike ride? The Kilianipark is one of the stops on the Gera cycle trail (northbound).