East of Leeds, off either J45 or J46 of the M1 (the new bit linking to the A1). It's very well signed (the brown tourist signs).
http://www.leeds.gov.uk/templenewsam/visitor/v isitor_where.html
From the CleckHuddersFax triangle, head East (towards Leeds) on M62, leave at J29, onto M1/M621 North (towards Leeds), be sure to follow M1 (left lanes!) heading to A1/Wetherby (NOT M621 to Leeds City Centre!!) and get off at J45 or J46, following brown signs.



