The Stonehenge landscape is a UNESCO World Heritage site containing not just Stonehenge but Woodhenge, the Durrington Walls Superhenge, Neolithic barrows, the Cuckoo Stone and a 3km Avenue created 4000 years ago which connected Stonehenge to the River Avon.
This 5 mile circular walk includes all of the above and is entirely legal and free, with not even parking costs. Woodhenge is free anyway, but Stonehenge costs about £20 per adult and parking can be £5 per car there, making it an expensive place to visit. The walk does not include access to the visitor centre, but it does get you close to the stones. It is well worth doing if you don't want to be herded around the stones with the thousands of other visitors, and if you want to see the site in its wider landscape.
Many visitors to Stonehenge regard it as an isolated place, a circle of stones that they visit and check off their bucket list before they drive on to the next place. Most remain entirely unaware of its place within the wider landscape - acres of windswept chalk grassland which was once home to a prehistoric community who altered and sculpted this landscape to a place of deep significance and ritual.
You will understand far more about Stonehenge by walking through those same grasslands, seeing the barrows where they buried their dead, the places where the builders of the stones lived, walking on the same ceremonial path they did to approach the stones over 4000 years ago, than you ever will from a bus ride from the visitor centre to the stones.
The swarms of tourists flocking around the stones, being pushed along by the will of the crowd, will look like colourful, scuttling ants as you approach from afar, unenlightened followers of the conventional, who exit through the gift shop clutching their Stonehenge branded souvenirs with their blinkers still firmly in place.