The event will last from 12noon to 5pm and will also feature live music, a birds of prey display and tours of the Castle, although numbers will be limited.
Swansea Council supported by the Friends of Oystermouth Castle has organised the fun as part of the Swansea Bay Summer Festival.
Inside the Castle there will be the opportunity to meet the Ostreme Players Lady Alina when visiting the maze of dark vaulted chambers and newly discovered secret spiral staircases that haven’t been explored for hundreds of years. There will be a discounted charge of £1 entry on the 16th with 5s and unders free.
The re-opening celebrations will mark the near completion of a major conservation project funded by Heritage Lottery Fund, the Welsh Government through Cadw, Visit Wales and the European Regional Development Fund with support from the Friends of Oystermouth Castle.
Visitors will also be able to discover the depths of the central block cellars for the very first time and enjoy interpretation that's being added to tell the castle's story. This includes a visit from King Edward I in 1284 – also known as Edward Longshanks.
Andrea Clenton, Project Development and Funding Manager at Swansea Council, said: “The conservation works are now reaching their final stages and their completion will allow better access to many more parts of the castle than ever before.
“It’s an attraction that’s steeped in fascinating history that will offer an educational and fun visitor experience for people of all ages.
“The re-opening event is going to be a real treat. It will give hundreds of people an up-close encounter with a medieval tournament that would once have attracted hundreds of the finest knights from across Europe.”
New visitor facilities, an educational space and a 30-foot high glass viewing platform and bridge that leads to Alina's Chapel were introduced in time for the castle’s first phase opening last summer. Over 12,000 people made a visit to the Castle between July and September.
Other events planned at the attraction this summer include an archaeology day during National Archaeology week and a medieval living history day with the Friends of Oystermouth Castle.
Have a look at www.swansea.gov.uk/