If there's something like the ultimate infinity pool, I'm pretty sure it's located at the Marina Bay Sands resort in Singapore. The hotel in itself is already quite bizarre: it's the most expensive hotel in the world at about 5,2 billion pounds (which is about double of the former record-breaking hotel, the Emirates Palace Hotel in Abu Dhabi).
The Marina Bay Sands has 2,560 rooms, costing from $500 a night upwards. That's quite impressive. Then, it has a casino, a museum, a theatre, a convention centre and indoor canals. Even more so impressive.
But the most impressive part of the hotel is, in my eyes, the so-called skypool, spanning the top of the three towers of the hotel, at the 55th floor. The pool itself is about three times as long as an olympic size pool, and seems to end in the air. That's because the water flows over the edge into a catchment, situated a bit lower. It's pretty spectacular to be able to swim on the 55th floor, with the skyline of Singapore in the back, and not to have a (visible) edge between you and the surrounding.
The complex is designed by Moshe Safdie, and I found it via the Daily Mail website.