The construction of Poundbury, Dorset, began in 1993
Ramblers have claimed plans to expand the Prince of Wales' model village with 1,200 new homes and a primary school would create "an urban ghetto".
South Dorset Ramblers has objected to an application from the Duchy of Cornwall - Prince Charles' private estate - for Poundbury, Dorchester.
The group says the plan would force residents on to busy roads and cut off access to the countryside.
But the Duchy of Cornwall said the claims were "misleading".
Peter Evans, from South Dorset Ramblers, said: "It is shocking that we have ended up with proposals that hinder walkers when the prince himself said he wanted a plan that put the pedestrian at the heart of the design, instead of the car."
Campaigners fear that if the proposals are approved by West Dorset District Council people will have to drive to the attraction because there will be not be an easy pedestrian route.
Poundbury, which was created in 1993, is an urban extension to Dorchester and was built by the prince to encourage greener ways of living.
It is home to 1,500 people, with plans for developing housing for about 5,000 people and creating 2,000 jobs in the factories, offices and general facilities across the site by 2025.
The village is close to Maiden Castle - an Iron Age fort that is considered by English Heritage to be the finest in Britain.
Much of the land around the castle is owned by the Duchy and a tenant farmer whose holding lies close to the attraction.
He has objected to calls for greater access to the land he works.
A spokesman for The Duchy of Cornwall said: "The Duchy of Cornwall has already created the Causeway Walk linking Poundbury to the principal access to Maiden Castle.
"The current proposals are for the use of two agricultural underpasses so the public can cross the Dorchester by-pass safely.
"The tenant farmer has been very accommodating in offering public access, but cannot offer everything the ramblers have asked for."
The spokesman also denied that the village was isolated.