For thousands of years, very little was known about Venus. It appeared on the sky in the morning and in the evening. The way it, like Mercury, swiftly moved against the background of static stars suggested it was a planet. And, it's brightness, third after the Sun and the Moon, meant that it was bound to be of decent size, and rather close to us.
Venus got her name due to this brightness. She caught your eye and was, I imagine, thought to be beautiful. And so, she was named after the Roman goddess of love and beauty. Aphrodite to the Greeks, Ishtar to the Babylonians.

The first person to look at Venus through a telescope was Galileo, in 1609. All he could see, however, was a featureless disk. As optical telescopes got bigger and more widespread, that was all anybody could see. No surface, no details. Venus, it seemed, was completely enveloved in an opaque layer of thick clouds. For a few centuries more, this was all we had. How thick are those clouds? What do they consist of? What lies beneath them? Nobody knew.
This, perhaps not too surprisingly, led to imaginations going wild, and an influx of various ideas: there might be jungles on Venus, scientists suggested. Or swamps, perhaps. With clouds that thick, there should be plenty of water vapour in the air, and thus a wet surface. Maybe there were even dinosaurs there. As always with a thing we know nothing about, the Venus case was open to the wildest speculations.

In general though, ideas and suggestions were benign in nature. Since Venus is so close to us and of almost of the same size and mass as Earth, we nurtured the idea of Venus being a kind of sister planet. A balmy, summery Earth, where things were a little warmer and a little greener due to it being closer to the Sun. With the arrival of spectroscopic analysis, though, it became possible for us to, without going there, measuring the properties of the Venusian atmosphere. This was done in the 1920's, and the result showed carbon dioxide. Lots and lots of it, without as much as a hint of any water vapour.
This didn't do much for the scientists at the time. The swamps were abandoned, and it was proposed that with so much carbon dioxide in the atmosphere, the surface must be full of carbon compounds, making Venus a planet covered with petroleum. Or, as some who refused to believe in an absence of water claimed, the atmosphere might be dry, but the surface could still be wet. With so much carbon dioxide in the atmosphere, the water had to be carbonated. Venus would have veritable oceans of mineral water.

As it turned out, we would have to wait for an answer until the 1960's, when Russia launched its Venera program. The first probe aimed to touch down onto the surface of venus, Venera 3, was designed for an atmosphere somewhat like our own, and was subsequently crushed like a tin can before returning any data. Venera 4, 5 and 6 came in various states of reinforcement, but none of them lasted even an hour. They did get a chance to sample the Venusian atmosphere however. It was, as predicted, full of carbon dioxide, while the clouds themselves turned out to be, not water, but yellow-stained masses of concentrated sulphuric acid.
Farther down, there were increasing amounts of sulphur dioxide. Pressures here become so high that the early Venera spacecrafts malfunctioned. It was in 1970, through Venera 7, heavily reinforced much like modern submarines, that the Russians became first with successfully landing a spacecraft on another planet.

It turned out that temperatures on the surface of Venus were as high as 740K (~470°C), hotter than any household oven, and hot enough to melt lead. The pressure of the Venusian atmosphere is 90 times that on Earth (about the same as the pressure at a depth of thousand metres in an Earth ocean). The air is so thick that to an observer on the surface of Venus, the ground, although solid and rocky, would seem to ripple, and distort. If unprotected, the very same observer would be boiled in the heat, fried by the acidic air, and crushed by the pressure in less than a second. Of all the known places in the solar system, this beautiful evening and morning star is the one that most closely resembles our idea of hell.

So what happened to Venus? It's twice as far from the Sun as Mercury, but hotter still. It is due to a phenomenon very well known on Earth today: the greenhouse effect. The Venusian atmosphere, full of carbon dioxide, lets in the visible light from the Sun, but will not let the infrared heat-radiation generated by the surface escape. So the temperature keeps climbing, until what little infrared radiation that manages to get out just balances the sunlight absorbed by the surface.
Today, we know that Venus is by all accounts, very far from the lush, balmy Earth-like world first imagined. To me it seems to serve as a cautionary tale of what could happen to a world, not too unlike our own in location or mass, when the greenhouse effect goes out of control. After all, in a cauldron like Venus, there's not likely to be anything alive, even creatures very different from us.