Thanks again to my hotel - letting me use one of the bicycles for free the entire day - I went on a trip to Stora Delsjön lake, the biggest lake in Göteburg. And it's only 20 min away from the city center by bike! You bet, I couldn't resist the idea :-)
The nature there is wonderful; it's very wild but with convenient hiking paths all around.
I'm at a loss for words to describe the amazing moment I had there - wished I could have stayed longer...