Venus is a hellish, uninhabitable planet that has undergone a runaway greenhouse effect.
Venus has almost no liquid water due to extreme temperatures, and any past oceans likely evaporated billions of years ago, worsening the greenhouse effect.
On the surface of Venus, temperatures can be up to 500° C (hotter than the boiling point of lead) with an atmospheric pressure over 90 times greater than that of Earth's—this would be the equivalent of standing (and getting crushed) underneath 1km of ocean water on Earth.
The lower portion of Venus' atmosphere is comprised of hurricanes, lightning and perpetual rainstorms of sulphuric acid.
Despite these immense challenges, there are possible steps that could be taken to terraforming Venus in the far future.