Xel'naga temple

A Xel'Naga Temple is an artifact, created either by Protoss or Xel'Naga, found on various worlds. Some Temples have special functions. They are commonly created over a powerful nexus of cosmic energy. The most renown Temple was created by the Xel'Naga on the world of Shakuras; it was used by the Dark Templar to destroy the Zerg which had infested the world.

Temples of Aiur
The first Protoss Temple on the Xel'Naga-engineered world of Aiur was built long ago on a nexus of cosmic energy (the same type of energy used by the Dark Templar and the Zerg) and marked the spot where the Xel'Naga first set foot on Aiur.

It was destroyed by the Zerg so the Zerg Overmind could manifest itself physically on Aiur. The Overmind said of it: "Behold, there is a temple, not far from here, that lies upon ground most hallowed. Though I have born witness to the passing of countless millennia, the temple which you must assault is older by far. For it was constructed by my creators, the Xel'Naga, and it marks the site where the Xel'Naga first set foot upon Aiur."

Ziggurat
The Ziggurat is a Protoss Temple on Aiur discovered by the Terran xenoarchaeologist Dr. Fredrick Thompson, who had this to say about it:

"I can't believe my eyes. I finally found what I had been looking for all this time on Aiur. After evading the Terran blockade and quarantine of Aiur, dodging countless Zerg patrols both on the ground and in the air, and starving for the last two weeks, I've finally seen my dream take shape before my very eyes. I've found the Ziggurat, and it's more beautiful than I can imagine. I can die now a happy man."

-Final Transmission of Dr. Frederick Thompson, Xenoarchaelogist.

Temple of Bhekar Rho
The Terran-colonized world of Bhekar Rho is home to another Xel'Naga Temple. It was unearthed due to a powerful windstorm and activated when a Terran approached too closely. The Temple absorbed him.

The Temple was surrounded by Khaydarin Crystals and appeared to be organic. Studies on the Temple were limited due to a battle which erupted among the Terrans, Protoss and Zerg; all three races sent members within the Temple in an attempt to learn its secrets (and prevent the other races from gaining any information from it). The Terrans dropped a nuke on it, but the Temple absorbed the energy and reached its full potential, absorbing the nearby Zerg and Protoss but "discarding" all of its Terran victims (who emerged alive). The top of the Temple was blasted open by an "energy creature" which may have possessed the essences or genetics of both Zerg and Protoss.

Temples of Braken
The Temples of Braken were destroyed during the recent conflicts. It is associated with prophecies which claim that "he who harnesses this world will someday wield great a power, sanctified by the ancient ones". This could be a reference to the Xel'Naga.

Temple of Nemaka
The Temple of Nemaka was discovered fifteen years before the events of StarCraft: The Dark Templar Saga: Firstborn but was only briefly recorded by bored Marines. At that time, the Temple was "alive" with a green glow. It was surrounded by dozens, possibly hundreds of Khaydarin Crystals.

Fifteen years later the Temple was investigated by Jake Ramsey, an archaeologist hired by Valerian Mengsk. By this time, the Temple was dead, at least on the outside, and something had cracked open the top from the inside (possibly the same type of energy creature seen on Bhekar Rho). Ramsey entered the Temple using oval-shaped holes and eventually used the Golden Mean formula to enter its heart. There he found the near-dead Zamara, a Protoss mystic, who planted her memories (and many others) into his head. Ramsey fell ill and the planet was abandoned by the Terrans.

Temple of Shakuras
Another Xel'Naga Temple was found on Shakuras, current homeland of the Dark Templar. Again, it was built on a nexus of cosmic energy. It consisted of a pyramid-shaped structure with a small floating crystalline top, and appeared very different (and larger) than the Temple on Aiur. Through the use of the Khalis and Uraj Crystals, Artanis and Zeratul were able to use the light and dark sides of Protoss psionic energy to activate it, and scour the Zerg from the dark world.

The Xel'Naga Temple did not have a psionic shield during the game, but it did during the cinematic as the Zerg attacked it after it was activated. Most likely the shield could only activate when the Temple itself was activated.

Theories about the Temples
Very little is known about the Temple on Aiur, but the second Temple had a few clues:

First was the use of cosmic energy. It appears the Xel'Naga, a race which had at least some psychics (and used psionic technology such as Khaydarin Crystals), but this energy is opposed to the "purity of essence" used by the Khalai. This is the same energy used by the Zerg and Dark Templar.

Through study, the Dark Templar knew that the Xel'Naga Temple could destroy the Zerg, possibly through the use of cosmic energy, but why was the light side of Protoss psionics required as well? Possibly the Temple was supposed to be used by Xel'Naga and Protoss working together to attack the Zerg. The Temple only affected Zerg on the planet, though.

The Temple was not reactivated in Drawing the Web but could be reactivated in Enslavers: Dark Vengeance, which took place before Drawing the Web.

Some fans of the game claim you can see "bugs" in the Temple. While the Zerg are "bugs", these bugs didn't resemble any known Zerg breeds. No one knows what the Xel'Naga look like, but it's likely they are not humanoid in form (since they're not pure of form, and the Protoss are humanoid in form). It's possible these "bugs" were representations of the Xel'Naga.

Trivia
In the older, pre-release version of StarCraft, the Temple was a Protoss structure which created Archons. The building was removed from the tech tree when the method of creating Archons (merging two High Templar) was changed.