It is possible to reach the Grassi hut on the MTB, either from Valtorta (Val Brembana, Bergamo) or from Barzio (Valsassina, Lecco). Both Valtorta and Barzio have the possibility to complete a round.
In both cases, these are difficult paths, only for experts, with a lot of pushing, especially when climbing!
Good descriptions (in Italian) and GPS tracking can be found on various pages, such as: www.moonrider.it, www.mtbinvalbrembana.it, www.valbrembanaweb.info, www.pieroweb.com (for the Valtorta circuit) or www.paolo-sonja.net for the tour around Barzio / Valsassina.
We are happy to provide some information on request, in German or English.