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Venus - The Earth's twin
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At a glance, Venus and the Earth have many similar traits. They 
share almost the same size and weight, both orbit relatively 
close to the Sun, and contain similar amounts of several key 
elements. Before short-ranged observations of the planet 
occurred, many people speculated that the pale yellow clouds of 
Venus hid a warm, wet planet teeming with life. Nothing could be 
further from the truth.

Venus is a dry and lifeless sphere.  Long ago carbon dioxide in 
the atmosphere trapped the heat of the sun, boiling away what 
may have been huge oceans.  Volcanic eruptions on the surface 
filled the skies with clouds of sulphuric acid, which gust 
around the planet at speeds as high as 360 kilometres per hour. 
The thick atmosphere pushes down on the surface with a pressure 
90 times greater than on Earth (As much pressure as felt by a 
submarine at a depth of 3000 feet).

If you could survive the suffocating temperature and pressure 
and walk on Venus you would notice a strange phenomenon - 
distant objects would be distorted, and you would be able to 
see beyond the misshapen horizon of the planet. The abnormally 
thick atmosphere tends to refract light towards the surface of 
the planet, and this curved light would result in a bizarre 
'fish eye' perspective of Venus.

Radar observations have managed to penetrate through the dense 
clouds to reveal an extremely smooth surface, lacking any deep 
ravines or large mountain ranges. There is evidence of craters, 
formed when large meteorites crashed through the dense cloud 
cover, as well as some geological activity.

Every planet in the solar system has strange and unexplained 
features, and in the case of Venus it's the spin. Venus is the 
only planet which spins backwards, all the others move in the 
same direction as their orbit. This unexplained feature might 
be due to gravitational interactions with the Sun, which slowed 
the spin to its current value of 243 Earth days.

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Images
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1.  The surface of Venus from space
(http://www.solarsystem.f2s.com/venus/img1a.jpg)

This beautiful image of Venus is a mosaic of three images 
acquired by the Mariner 10 spacecraft on February 5, 1974. It 
shows the thick cloud coverage that prevents optical 
observation of the surface of Venus. Only through radar mapping 
is the surface revealed. 

© Calvin J. Hamilton

2.  Venera 13 on the surface of Venus
(http://www.solarsystem.f2s.com/venus/img2a.jpg)
This image was taken on March 1, 1982 by the Venera 13 lander. The 
spacecraft only survived on the surface for 2 hours, 7 minutes, but 
during that time it was able to send 14 images on the planet's surface. 
Part of the lander is visible in the bottom right of the image. 

Public domain image. 

3.  Computer simulation of the surface of Venus
(http://www.solarsystem.f2s.com/venus/img3a.jpg)

Computer generated three-dimensional view of the surface of 
Venus. Radar data was combined with images recorded by the 
Soviet Venera spacecraft to create a virtual landscape.

Public domain image courtesy of NASA.

4.  Radar image of the surface of Venus
(http://www.solarsystem.f2s.com/venus/img4a.jpg)
This global view of the surface of Venus was created from a combination 
of data from the Magellan radar mosaics and the Pioneer Venus Orbiter 
data. Colour pictures from the Soviet Venera 13 and 14 spacecraft were 
used to estimate the surface colour. 

Public domain image courtesy of NASA.