There is also Dove Holes, bit longer on the train, but you get a henge and a couple of barrows (about 20mins walk from dove). Plus a further 45 mins on from them a hillfort...
Hmm, good thought. Don't necessarily want to stray too far though, in case of transport disaster. And I've just discovered that return to Broadbottom is £3.90 (off peak), so nice and cheap too.