Mercury is the small planet closest to the sun. It is small so that strong gravitational force wouldn't be a problem for landing as would be the case with for example Jupiter. But it is so close to the sun that intense radiation from the sun would be problematic. Mineral sources might be a possible reason to go to Mercury. Certainly one would also assume that before interstellar travel humans would have visited this close planetary body in the solar system.

PIA02422
Ridges and Fractures on Floor of Caloris Basin
NASA/JPL/Northwestern University

PIA03101
"The Mariner 10 spacecraft imaged this (southern hemisphere) region during its initial flyby of the planet. The Mariner 10 spacecraft was launched in 1974. The spacecraft took images of Venus in February 1974 on the way to three encounters with Mercury in March and September 1974 and March 1975."
NASA Photo Journal:http://photojournal.jpl.nasa.gov

Numerous craters very similar to the moon's surface can be seen in this image.

The crater in the middle of this image is 6 miles in diameter. "Mercury's surface is similar to that of Earth's moon, where a history of heavy cratering is followed by volcanic filling."

A good place to find facts and information about Mercury is:
Planetary Data System Imaging Node:
www-pdsimage.jpl.nasa.gov/PDS/

Venus is clearly visible in the night sky. Many people observe it with the aid of a telescope. It is very hot and inhospitable. Special imaging technoques are required to get a better view of this planet. Some dream of changing its dense cloud layer to reduce the heat and make it livable. That won't happen any time soon though.

PIA00104
Venus - Computer Simulated Global View Centered at 180 Degrees East Longitude

PIA00159,USGS
Hemispheric View of Venus Centered at 180 Degrees East Longitude

http://antwrp.gsfc.nasa.gov/apod/image/0107/mars_hst_big.jpg