Pre erasmus trip

Hiii, i’m beginning an erasmus in Denmark mid august and I wanted to take advantage of my trip to visit other destinations during my interrail. I have a six days for 6 months type and was thinking of using two days to travel to Denmark and then visiting Berlin on the road but i’m not sure. So I’m asking you what would be a nice itinerary from Belgium to Denmark as a solo traveller (it’s my first solo trip so if you have advice for that too :))