At Gunwharf Quays the hotel and the casino floor are separate buildings on one named estate, which lists both in its own directory.
Spinnaker Tower lit up across Portsmouth Harbour in the evening
Holiday Inn Express stands on The Plaza; Grosvenor Casino Portsmouth Gunwharf Quays is in the Central Square South Building. The hotel's own site does not mention the casino, so the estate directory is the link. The casino floor is open 24 hours, with live tables from 1pm to 4am, and to 5am on Fridays and Saturdays. Your first visit starts with a free one-time sign-in with photo ID.
Portsmouth Harbour station is 0.2 km away in a straight line, at the edge of the harbour itself. Southampton Airport is 25 km off, straight line; the hotel gives about 25 minutes by road. If you drive, the estate car park gives hotel guests the first 24 hours free and charges for later days; it has 35 accessible bays beside the lifts.