Above is a photo of an «O» theatre, with it's stage of pool in the foreground. This photo was obtained from cirquetribune.com.

For those of you who have not seen «O» ... I am sure you'll find these facts pretty fascinating. For those of you who have seen it, hopefully you'll get a better appreciation of the show after you've read this trivia.
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Premiered in: October 1998
Number of spectators since opening: Over 6 million
Number of artists: 85
Number of countries represented in cast: 23
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«O» cost about $100 million to produce and it took 20 designers three years of testing and development that resulted in this one-of-a-kind aquatic environment. A 20 by 30 foot test pool was first built to determine the affects of various materials in a theatrical setting.
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The «O» pool measures 150 x 100 feet at the widest points and is 25 feet deep.
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«O» theatre seats 1,800 people. The height from the bottom of the pool to the top of the high steel in the grid is 145 feet, the equivalent of a nine and a half story building.
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There is an invisible wall between the stage and the audience generated by air jets; the goal is to control the two temperature zones in the theatre. The stage is kept at a higher temperature while the audience area is kept at a lower temperature. There is a temperature sensor every few seats in the theatre to ensure the audience is always comfortable. The wire mesh theatre dome acts as a chimney allowing the warmer air to escape.
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All of the 150 technicians and cast members (with the exception of contortionists and musicians) have scuba certification; 14 technicians work permanently underwater during every performance.
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The water is kept at a comfortable 88 degrees. The pool takes 12 hours to fill and the sophisticated filtering system cleans all 1.5 million gallons of water three times a day (with each filtering process taking about 6 hours).
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The «O» pool is drained once a year for maintenance and the water is channeled into the huge lake-like fountain of The Bellagio resort, which causes the water level of the fountain to rise by an inch.
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The pool contains seven sophisticated hydraulic lifts to make a conventional stage surface that may be puddle-like, dry, or retracted to create other shapes. The surface of each of those seven lifts has about 5000 tiny holes; this allows the platform rise and fall freely in the pool.
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There may be as many as 20 performers beneath the water at once waiting to enter from above, emerge from below or exit into the wings. They are always watched over by 16 scuba divers. Two of those divers are outfitted in surface supplied AGA full-face masks with communication systems.
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The complexities of this underwater scene, given the moving lifts, often working in the dark, and the fact that of so many performers are coming and going, makes the «O» pool seem like a busy underwater street corner.
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There are 800+ cues during the show (mostly audio tones and lights) and they must be kept in perfect sync. If a certain scene becomes out of sync, it is the underwater scuba divers who give signs to regulate the tempo back to its focal point.
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6000 feet of perforated hose is configured in the pool bottom to produce an air train that both hides underwater activity and creates transitions for actors to emerge and, of course, submerge. To minimize sound disturbance caused by waves, the pool is surrounded by a series of gutters containing various size pebbles.
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In addition to the topside sound system, the pool has twenty-three underwater speakers with an additional speaker known as a Rover, used when the aquatic masking is active so the performers and divers can still hear cues and music.
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During the show, a total of 1815 lights and 230 colour scrollers provide 4 million watts of light.
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The control room stuff up above in the theatre keep a close eye on the underwater activities via three underwater video cameras. 26 other video cameras provide different above-the-water views and 39 video monitors are located back stage.
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In case of an accident, there is a red emergency stop button called E-STOP, which, when pressed, shuts down all electrical and mechanical equipment. It has never been used since the show premiered (and hopefully never will be).
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Nearly a dozen performers from «O» have taken part in the Olympic Games; some are gold medalists.
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Prior to premier, the artists went through 12 months of intensive rehearsals.
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The synchronized swimmers are world class Olympians coached by former Canadian gold medalist Sylvie Frechette.
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The umbrella that the "guide" rides on the water is a fully motorized boat. It has a propeller in the bottom and is steered by rotating the handle portion of the umbrella.
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The horses that the "red guards" ride in the show are also motorized boats driven by a joystick. Each horse weighs approximately 750 pounds.
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The crocodile mask, which can carry nine performers, is operated by a technician underwater.
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The movable Barge is 1.5 tons of fiberglass and foam. It maneuvers into place with the aid of seven technicians, holds 20 performers, and has 14 breathing stations on its undercarriage for artists who must remain submerged during extended periods of the performance.
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During every show, some performers have multiple sets of costumes so they may reappear dry despite having been in the water.
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Due to wear and tear, the costumes in «O» need to be replaced often. Multiple costumes per performer per year cost a few thousand dollars to produce.
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Throughout two shows each day, «O» wardrobe staff does 65 loads of laundry.
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«O» artists use wax-based makeup, which can last in the water for the duration of the show (with minimum touch-ups in between the stage appearances).
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«O» has a live orchestra, which is shielded behind the glass in order to protect the instruments from the moisture. Some of the musical instruments used in the show are more than 100 years old.
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The strange string instrument in the soundtrack of «O» is an Erhu, a traditional Chinese violin.
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«O» songs, just like in many Cirque du Soleil shows, are sung in an invented language that many people refer to as "Cirquish." The words have no literal meaning, therefore, each person experiencing the show can interpret these phonetic sounds in whatever way their emotions lead them to.
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«O» is performed at The Bellagio hotel in Las Vegas twice a day: at 7:30pm and at 10:30pm. There are no shows on Mondays and Tuesdays.
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Hope this explains why tickets for «O» - depending on the seat - cost $150, $125, or $90. And despite the price, they are STILL hard to get!!!
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Please note that the facts above are obtained from various sources, including worth-of-mouth, printed publications and the Internet. I have no way of guaranteeing their precise accuracy and, therefore, I do not recommend the use of this space as a quotable reference.