The cash for Cefn Coed Colliery Museum adds to £1.5m already promised to renovate the site.
It is one of 11 places receiving a total of £6.6m to boost visitor sites in the south Wales valleys.
Plans for bike paths in Dare Valley Country Park will receive £803,600.
Cefn Coed colliery in Crynant near Neath – once the world’s deepest anthracite coal mine – opened as a museum in 1978.
Earlier this year local councillors had branded the site a “dump” – with one saying it had looked closed since its winding gear was dismantled and left to rust.
The £1.8m of cash will be used to build a timber-framed structure for a visitor centre, a play area and cafe, and adds to £1.5m pledged by the Welsh Government for restoring the winding gear.
On Wednesday the Welsh Government announced £6.6m for what it has called “discovery gateway sites” as part of its plans for a Valleys Regional Park.
The project aims to use the natural and cultural heritage of the region to generate social, economic and environmental benefits.
The cash includes £900,000 for a visitor centre at Parc Penallta near Ystrad Mynach, £803,600 for family-accessible bike paths and laser tag at Dare Valley Country Park at Aberdare, and £700,000 for Cyfarthfa Park, Merthyr Tydfil.
Bryngarw Country Park, near Bridgend, will receive £500,000, which includes cash for a new education centre, and improvements will be made at Parc Bryn Bach in Blaenau Gwent with £500,000 of funding.
Caerphilly Castle will get £150,000, Pontypridd’s Ynysangharad War Memorial Park £296,398, and the Blaenavon World Heritage Centre £180,000.
A scheme for a space for classes, office space and discovery trails at Cwmcarn Forest will be given £450,000.
The Welsh Government said the £6.6m investment in the sites, planned to be spent between now and 2021, will help “provide safe and welcoming spaces that can be enjoyed by the local community as well as visitors from further afield”.