First series: mountains of doom one where they are on the Brecon
Beacons with Brian Blessed and the hermits :)
Second series: either the poltergeist one or the island of doom one
(I think that one makes me the saddest, as I still haven't seen the
last of series 1)
I still need to see series 2 again to make up my mind though, haven't
seen it enought times to remember them properly.

Kim