A locked route in Panshanger Park is to be opened almost five years after it was promised.
Developers Tarmac have announced that the Mimram Valley walkway and 4.7km of new paths will be opened on June 24.
Michael Charlton of Tarmac said: "We are pleased to announce the opening of 4.7km of new footpaths at Panshanger Park to improve access from the south of the park and provide access to the Cole Green historic landscape.
"The Mimram Valley path will also be opened to provide an additional east-west permissive route in the park through the lower valley to the south of the River Mimram."
Previous reasons for the path remaining closed have included the requirement of a fence and to prevent dogs interfering with river fly larvae.
Mr Charlton added: "Between now and the path opening, we will be completing the new fencing to protect the River Mimram, along with acclimatising the longhorn cattle and their calves to the park before they enter fields that are open to the public.
"As the Mimran Valley path is located within a nature reserve, it has taken time for us to find a sensitive solution that enables the public to enjoy the route, whilst protecting the delicate ecology of the River Mimram and preserving the historic value of the park."
Welwyn Hatfield MP Grant Shapps said: "Whilst this is good news, Tarmac has twice previously promised its opening without doing so and with no explanation given. I'll therefore be keeping a close eye on this and will be meeting with Tarmac in the coming weeks to make sure they finally follow through on their promise."
Will Davis, chairman of WGC Society, said: "The WGC Society and Friends of Panshanger Park are very pleased this now happening, it is a step towards finally seeing our new Country Park fulfill its potential as a wonderful outdoor amenity for the residents of Welwyn Hatfield."
Tarmac and partners will monitor the use of the Mimram Valley path over the coming months to ensure ecology and biodiversity is not affected by public access to the route.
More of the site will be opened up in a series of carefully managed phases as the remaining extraction processes on site come to an end.
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