The tour is not strenuous, but you do have to get yourselves to the Visitors Centre very early, you must have closed in shoes i.e. sturdy trainers or walking boots, and they suggest you take water with you as it can be very hot (although it rained when I went!!) They are very strict on the numbers they take, and you cannot just turn up on the offchance of getting the tour - I believe they also need to see your passport too. Oh, and the trip is free too!!!! Good luck
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HTH
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Edited to say, I think there are two walking trips - the one I went on is the "easy" route! I believe the other one is marketed for serious hikers!!!!