Terrible idea: a scifi story set in a early-20th century idea of the solar system.
Mars is a dying desert covered in canals to bring water from the poles to the sand cities at the equator.
Venus is a humid jungle/swamp full of strange beasts.
Both are fully habitable by humans with no more gear than you'd need to cross the Sahara or venture into the rainforest.
The trick? This is actually a distant future realistic setting. We terraformed the planets specifically to be like that.