Zenith

Zenith is Tecna's home world. It is the Realm of Technology in which it is filled with an extremely heavy use of technology, electronics, machines, and gadgets. The people and inhabitants enjoy a high and peaceful standard of living. They also use the metric system.

There are oceans like every other inhabited planets and Lithia is the Selkie who guards Zenith's ocean gate.

Royalty
According to the Winx Club comics, Tecna is the Princess of Zenith and her father is the King. It is unknown if she is the Princess of Zenith, or even a princess in the animated series at all. The King of Zenith appears in episode 18, attending the meeting in Domino, his name is Cryos.

Data Bridge Castle
It is a castle in Zenith's Ocean, where the Gem of Empathy was located in.

Season 5
In Season 5, The Winx travel to Zenith in search of the Gem of Empathy. Tecna bonds with Lithia, the Gatekeeper of Zenith's Oceans.

Trivia

 * The word "Zenith" is generally used to describe a point supposed to be directly above a particular location. In astronomy, it denotes the highest point a celestial body reaches in the sky (for example the Sun reaches its zenith at noon).
 * Zenith is known as "Titania" in the comics. The planet Neptune has a moon named Titania.
 * It was learned from Tecna that Zenith's people don't show their emotions. Ironically, the Gem of Empathy is located in their planet.
 * Zenith appeared physically for the first time in The Gem of Empathy, in which the Winx acquired the Gem of Empathy in their quest for the Sirenix evolved transformation and tremendous magical power.
 * In the 4Kids dub of the series, it is called the Third Binary Sector.
 * The Zenith king appears in Winx Club Season 5 The Devourer.