As webtoe mentions, there are three actual theatres in the National Theatre complex on the South Bank, together with a huge shared foyer.
The Olivier Theatre
The Olivier is the largest of the three theatres in the building. It seats 1150 people in two tiers, shaped like a fan around the stage. The stage is therefore essentially round, although often it's used as a conventional stage.
What's most impressive about the theatre though is the machinery under the stage.
- Imagine a tall cylinder, sitting with its flat end on the ground.
- Cut it in half across the middle, horizontally.
- Cut it in half again down from top to bottom. You now have four equal semi-cylinders, two on the bottom and two on top.
- Take one of them away.
Now imagine that the whole contraption can be rotated round either at once, or just the top half or bottom half, and also that where there's a missing quarter, the piece above or below it can be raised or lowered into the gap. And all these rotations take place almost silently.
This is how the machinery works. Each of the three semi-cylinders contains a set (they are hollow so can represent the inside of a house). You're looking at one of these pieces. It rotates round, revealing the piece of scenery behind it. Then, while the play is going on, the first piece of scenery is lowered into the gap beneath it. The lower half rotates round, and a third piece is lifted behind what you're looking at. The top half then rotates, revealing the third piece. This allows for seamless changes of set during a play. Due to the layout of the audience, all these changes are 1) invisible and 2) inaudible to the audience. The entire mechanism can also be lowered under the stage to provide a flat surface.
The entire unit is about 60 feet high and the cylinder cross section is about 25 feet in diameter. It's also been notoriously unreliable, sometimes breaking down mid-performance, leaving the actors to apologise to the audience and sort out refunds.
The Lyttleton Theatre
The Lyttleton is a conventional proscenium arch theatre seating about 890 people with no restricted seats. Due to its modern design, it can be made into an open-end stage and an orchestra pit can be added for up to 20 musicians.
No seat is further away from the actor's point of command than the distance from the front row of the dress circle in many older, larger theatres.
The Cottesloe Theater
The Cottesloe isn't a conventional theatre, but more of a flexible workshop often used for experimental and new plays.
It's a basic room which has seats on two levels around three sides. If being used for a conventional play, a proscenium can be created at one end, and with the addition of seats on the floor, it has a capacity of 300. Alternatively, plays can be staged the round.
The Foyers
The complex also has a huge number of foyers. These contain the traditional bars and restaurants, but also a number of spaces for things such as piano recitals, performance art and exhibitions. These are usually free.
TenMinJoe says The Olivier Theatre is the only place I've ever seen the *stage itself* get a round of applause before there were even any actors on it. That thing is incredible.. I've never quite seen that happen, but it is damn impressive!