I live 5 minutes away from this "most important henge of its kind outside of Wessex". Unfortunately, it is most unimpressive but if you walk around the circle in the field and imagine what might have gone on all those years ago you will surely smile.
If you park in 'The Cock' pub car park in Old Lakenham and have a drink, and then walk over the river and railway bridges there is a footpath into the field in the direction of the henge. Follow the line of the hedgerow to the South along to towards the house. The henge is between two pylons to the left (east) of the house.
[visited 9/12/02] A perishingly cold december day couldn't temper the joy I had visiting this site. Really not much to see on the ground, just a depression with a low bank around it. It also has the pleasure of a fck off huge pylon right next to it..
But it's a henge, in Norfolk. And its even on the Norwich A-Z, Alan Partridge would be proud...
Arminghall is one of those sites that looks like nothing today, but in its time would undoubtedly have been pretty astonishing.
Like Woodhenge, its potential was spotted from the air by brave military pilot Gilbert Insall, who snapped it with his camera. Grahame Clark excavated it in 1935 - he found eight enormous post holes in the middle of the henge. Each was equipped with a slope to help manoeuvring (you can see these in the diagram posted by KK), and they were arranged in a horseshoe, with the open part next to the henge entrance.
The two holes that Clark excavated most thoroughly had post pipes nearly 1m across. Post pipes are the traces in the soil of rotted timber posts - so the oak timber posts must have been Enormous.
Considering Maud Cunnington thought her 85cm postpipes at Woodhenge translated into posts rising 7.5m above the ground and weighing 5 1/2 tons - well, Arminghall must surely have been a stupendous sight.
Though this may take some imagining considering its current environment.