Thanks to the full-planet survey by Magellan, we have data on surface topography to kilometer resolution for Venus. The deepest place known is the Diana Chasma in the Aphrodite region. It is 6500 feet ( 2 kilometers) below the mean surface of Venus. It is deeper than any similar feature on the Earth, and has much in common with the Valles Marineris on Mars. Venus also has other deep basins. One in the Northern hemisphere called Atlanta Planitia is about 4,500 feet or 1.4 kilometers below the mean surface of Venus.