There and back walk along the Purbeck chalk ridge (but then, what else can you do along a ridgeway?) Just over 5km (3.2mls) is you go the whole way.
Park in the car park at the top of Creech Hill. This is just before the start of the MOD Lulworth Ranges, so should always be accessible.
Head straight up the track signposted to Grange Arch and Corfe Castle. Soon after passing Grange Arch the track enters as fine a piece of un-improved downland as you are likely to find (contrast it with the 'improved' land on the other side of the fence).
Keep along the fence, and turn left through the gate; Creech Barrow Hill is straight ahead. However to get there, we have to wind our way down to the road, and the steeply up the side of the hill. A bit of a climb, but the view of the Purbeck chalk ridge winding away into the distance with its geological continuation on the Isle of Wight in the distance is worth it.
Not to mention the extensive views to the north over most Dorset and into Wiltshire.
Re-trace your steps to the car park, pausing to admire the fine view of Portland from the path opposite Grange Arch.
Grange Arch was built around 1745 by a Mr Denis Bond, the owner of Creech Grange in the bottom of the valley, presumably to enhance the view from the house. Personally I think the conversation went something like this:
"You won't believe it Ted, the boss has been to the Stately Homes Garden Centre and come back with a bloody great arch. Don't know where we are going to put it."
"Oh shove it up on the top of the ridge. Tell him it enhances the view; he'll buy that. He'll buy anything, come to think of it."