Used to go there every few months for work, only took the bike a few times as I got the impression that it was frowned upon! There are a few trails, there used to be a downhill course that was used for a world cup event years ago on the south side, but the drops on it were way beyond my skills, especially as I was on my own and the thought of dying of hypothermia with broken bones on a mountain side as I’d stacked it and no one knew where I was. There used to be a Riverside pathway to Castle Linderhoff (worth visiting anyways), I spent most time pounding tarmac, the climb back from Garmisch was a latic acid killer. Last time I was there was 5 years ago, so things may now be different, plenty of other stuff to do and see around there though, especially if you are willing to drive a little, I loved the area.