The Grotto of Thetis was designed as an outdoor ballroom, complete with marble flooring, tiered seats, and fountains running over stages of stones and shells. The grotto is also a component of Le Notre's clever hydraulics plan. As the sun goes down, the water in the grotto becomes illuminated, creating a beautiful sight that would have been appreciated by Louis and his guests. The design of The Grotto of Thetis was probably based on similar grottos that were built during the Renaissance period, especially in Italy. One of these is the Grotto di Neptune inside the Palace of Prince Charles in Turin, which was built for King Charles VI in 1443. Another is the Grotta del Leone (Grotto of the Lions) in Venice, which was built for King Charles IV in 1348. These two examples show that French kings were not the only ones to enjoy spending time in an outdoor ballroom! However, what makes The Grotto of Thetis unique is the use of sea shells instead of stone or marble. These are actually pieces of volcanic rock, but they look like sand dollars and other marine creatures when dried and polished. There are several places where you can see the remains of the original vegetation from which these shells were taken: you can see them engraved on some of the seats at Versailles.