Getting to the venue
By car
If you are coming by car, make sure to drive to a nearby parking parking lot. The official parking lot at the corner of Vechtdijk and Franciscusdreef (west of the fortress) is a good option, but make sure to NOT park here at night - it is not safe - lions and tigers and bears. Instead, if you want to park your car as well in the evening and at night, use the parking areas of San Cristobaldreef (north) or Costa Ricadreef (east). It is all free parking.
By public transport
Utrecht Central Station is easily reachable by train. From there, you should be able to take bus 3 towards the Franciscusdreef. From there, it is a short stroll towards the fortress.
By foot
Utrecht Sentral Station (and with that, the entire city center) is 4 kilometers away from the venue. If you like hiking, walking from and to the venue could be your thing too.
By bicycle
You could also opt for the Dutch thing: Riding a bike. There are quite a few options out there: At laagcatharijne.nl (Dutch only) you can rent very good bicycles for about 8,50 Euro per day. With OV Fiets, things become even cheaper (4,65 Euro) but you will need to get a (free) subscription first and a public transport pass, before you can take a bicycle with you. Note that in Utrecht Zuilen (the closest train station) there are little bicycles available. The option to cycle to the venue, is therefore best if you stay in the city center.