The Castle Park project in Bishop's Stortford has been awarded £1.94-million in lottery cash - one of six across the country.
The Heritage Lottery fund says they want to celebrate the health and wellbeing benefits of green spaces, as well as their history and community importance.
Sworders Field and Castle Gardens will be brought together to form Castle Park.
Conservation work will protect the ruined Waytemore Castle within its grounds, which dates back to at least the 1080s.
It was largely demolished in the late 14th Century but its Grade I listed remnants stand proudly in the landscape today as a precious reminder of Britain’s medieval past.
The remnants have been increasingly eroded by weather and foot traffic over the last century and were categorised as Risk 1, Priority A on the council’s Heritage at Risk Register in 2006.
Specialist conservation work will protect the ruins and allow for public access, lighting and new history information panels.
Other disused buildings in the park will be transformed into a park hub, which will include community rooms, café, toilets and a Changing Places facility (highly accessible toilet/changing room) and the River Stort, running through the park, will be rejuvenated to create a valuable wildlife habitat.
A series of community activities including archaeological investigations and tree planting will take place.