Location: Scottish Highlands, south west of Inverness Date built: formed during Caledonian oregony, c. 400 million years ago Designers/builders: natural feature Function: tourist attraction

Apart from anything else, Loch Ness is an impressive natural feature. Although it is the second largest Scottish loch by surface area after Loch Lomond, its great depth - 755 ft (230 m) at its deepest point) means it contains more water than every lake in England and Wales put together and more than any other lake in Scotland. The great depth means that Loch Ness never freezes. The reason is that, while the top 100 ft (30 m) of water reacts to the ambient temperature, below that level the water stays at a constant 44o F. As the surface water cools it sinks and is replaced by warmer water from the lower level. The Loch is fed by seven major rivers, while its only outlet is the River Ness, which flows through Inverness into the Moray Firth. 

However, what makes Loch Ness world famous is not its impressive statistics, but its elusive resident. The Loch Ness Monster (or "Nessie") has captured the public imagination, even though no scientifically verified proof of its existence has ever been obtained. The earliest reported sighting (albeit in the River Ness, rather than the Loch) was in the 7th century, when St Columba, using the sign of the cross, drove off a monster terrorising the local people. In 1933 the building of a road alongside the Loch brought more people to this hitherto remote area. Later that year George Spicer and his wife claimed to have seen a 25 ft (7.6 m) long monster crossing the road in front of them. Other sightings followed, some from respectable observers. In August 1933 a veterinary student said he had seen the monster and that it was a cross between a seal and a plesiosaur. In 1938 the Chief Constable of Inverness-shire, William Fraser, wrote that it was beyond doubt that the monster existed. In 1954 a fishing boat made sonar contact with a large object at a depth of 480 ft. Over the years, several expeditions, often with elaborate detection equipment - including one by the BBC in 2003 - have been mounted to seek out Nessie, but none has provided convincing proof. However, the legend adds to the spice of life and provides a steady stream of visitors to the area, so long may Nessie thrive.