Millions will be spent on South Quay site in Pembroke
About £4m will be spent on redeveloping the South Quay building in Pembroke.
The investment is part attempts by Pembrokeshire Council to turn the town into a top visitor destination.
Funding for the site next to the castle, which will include a visitor centre, comes in the form of £3m from the Welsh Government and £1m from the council.
The plans were announced on Friday at the "Visit Pembroke: Birthplace of Dynasty" event.
- Controversial St Davids Premier Inn gets go-ahead
- Princes Gate sale: Nestle buys Pembrokeshire bottled water firm
Paul Miller, the local authority's cabinet member for economy, tourism, leisure and culture, said the improvement of South Quay is "crucial for the regeneration of the town."
The plans are now subject to a final business case and agreement with local stakeholders before they can go ahead.