Just had a look on the map, its up the B480 from Henley, the hill from Watlington must go up from the opposite side.
I mentioned the Henley to Christmas Common route as it must be at least 3 miles long, similar to some of the long drags at Lanza (though the drag through Teguise to Haria is about 8 miles I think)
Just to add, these Lanza training rides are open to anyone who wants to join us, you dont have to be doing Lanza.