The Netherlands is flat. No mountains, a few hills. But still we call it mountain biking: cross-country, off-road biking through the dunes, special trails and (some) hills.
Bas de Koning, one of the Chief Editors of VATupdate, explains in a video how mountain biking and VAT are related. Hint: if the chain breaks, make sure you have a missing link with you.
Source: Less Grey (the video is in Dutch)
