This one looked complicated but it was actually very easy. We quickly found both sets of information and found the cache in the obvious place.
It was then that we noticed that Prof Tonks and Redirected Male had been here earlier today and we wondered whether it was them that we'd said hi to in the car park. We'd had to return to get something from our car (which by then they were standing next to) so we might have scared them off. If it was you two after all that I'm sorry we missed you.