Theodora's Resort is a miniaturized world located within a glass diorama sphere belonging to Princess Theodora.
Permanently set within a summer-like atmosphere, the diorama contains a summer tropical island and cabana located on top of a cliff at the center of the island. Within the island jungle is also a hot springs pool hidden amongst the fauna.
Following the revelation that Jack Rakan was going to enter the final rounds of the Ostia Tournament, Theodora offers her resort to Negi Springfield and Kotarou Inugami to train within to defeat the hero. With the tutorship of Headmistress Seras, Senator Ricardo and Evangeline's Scroll, Negi and Kotarou gain the power they need to win the tournament.
Some time later, the resort was used to contain Negi as his Magia Erebea began to run rampant. With the help of Evangeline's Scroll and his partners in the Ala Alba, Negi was able to overcome the darkness consuming him.
- Before their arrival to the Magic World, Evangeline A.K. McDowell trained Negi within another of these Diorama Spheres; this one being a mage tower with a tropical beach attached. She would also later reveal a series of larger diorama spheres which contained the Lebenschilt Castle; her castle from during the Dark Ages.
- During the opening hours of their attack on Cosmo Entelecheia's base within the Gravekeeper's Palace, it is revealed that the resort's diorama sphere is being kept aboard the Great Paru-Sama airfish.
- As an alternate world, time moves at an accelerated rate within the resort, where a single hour in the outside world is equivalent to a full day within the sphere.