Members of the Parliamentary Friends of Nature Group - one Liberal, two Labor and one independent - each said they were astonished that such world-class scenery was not already protected or promoted as a major tourist destination.

The MPs visited three sites along State Mine Road, north of Lithgow. The first was Marrangaroo Swamp, which is a superb example of the biological richness and beauty of wetlands that are a feature of the Gardens of Stone area.

Then they visited Carne West Swamp to see damage caused by longwall mining. The swamp died recently after longwall mining cracked surface rock, draining its water. The site was then incinerated during the 2019-20 Black Summer bushfires.

Finally, they went to a lookout with magnificent views of the Lost City pagoda rock formations.

Labor MLC Jo Haylen said the scenery "was truly magnificent, and we have to preserve it for everybody. Tourism is booming right now in our COVID environment. It's so close to Sydney and so magnificent - what an opportunity."

The state Shadow Environment Minister, Labor MLC Rose Jackson, told the media "it's a huge asset to our community here. We've got to do what we can to make sure that it's there to be enjoyed now and in future. It's just been incredible to see how beautiful it is."

Ms Jackson later posted on Twitter that the "Gardens of Stone is an incredible natural wonder just outside Lithgow and it needs to be better protected".

Liberal MLC Catherine Cusack, a former Shadow Environment Minister, said the Gardens of Stone "belongs to all Australians and they all deserve to see it".

Ms Cusack also warned that longwall mining was a significant threat to the region's wetlands and the pagoda rock formations.

"There is no more social licence as far as I'm concerned for undermining these sensitive areas," she said.

The visit was hosted by the Lithgow Environment Group, the Blue Mountains Conservation Society and the NSW Nature Conservation Council, all of which are part of the Gardens of Stone Alliance that developed the Destination Pagoda.

The plan, published in 2019, identifies the region's unique appeal.

"The ancient 'pagoda' landscapes above Lithgow are found nowhere else in the world, with their spectacular rock pinnacles, gorges, cliffs, waterfalls, swamps, forests, Aboriginal heritage and rock art, and many rare plants and animals," the document states.

"These features can create an iconic, rewarding, must-see destination for local people, Sydney residents and international visitors wanting to experience a different and special part of the Blue Mountains."

The proposal is to convert Newnes, Ben Bullen and Wolgan state forests into a State Conservation Area, with $32 million invested over 10 years in tourist facilities, including lookouts, platforms, road upgrades and signs.

Economic analysis has found the proposal would attract 420,000 visits a year to Lithgow, inject $40 million a year into the local economy and create about 260 full-time jobs.

Centennial Coal, whose Springvale and Angus Place collieries undermine the area, has declared its support for the proposal to declare the state conservation area if it does not inhibit mining operations.

A company spokesperson told the media last week "Our priority is ensuring the continuity of our mining operations, providing local employment and positively contributing toward the local economy and believe we can continue to do so if there were any future expansion of the Gardens of Stone."

NCC Chief Executive Chris Gambian said last week's tour was an historic moment in the campaign to protect the area because it was the first time a delegation of MPs had visited the site.

"MPs were surprised that such stunning scenery so close to Lithgow had not already been developed as a major tourist attraction," he said.

"Our hope is the MPs who have now seen the majesty of this place go back and tell the story of the Gardens of Stone to their colleagues in parliament.

"Many more people in Sydney need to experience the Gardens of Stone, one of Australia's great landscapes virtually on the city's back doorstep," Mr Gambian said.

"Many people have no idea there is scenery on the edge of Lithgow that rivals the best that Katoomba and Blackheath have to offer.

"This part of the Blue Mountains is largely unexplored by tourists simply for lack of investment in roads, lookouts and other facilities that could open these stunning landscapes to the world."