hell`s mouth is the route out or freiburg on the b31 to titisee read about it somewhere,shows some pics on google earth.last time i did it we then followed it all the way to the b33 and caught the ferry to rejoin the 31 again on to lindau then bregenz, l2,l4, b308, st2007,b310 past w**k(uses to be big road sign all brits had photo of.small one now) up to fussen