Uranus’s moon Miranda has features called coronae, at least one of which has a depth probably exceeding the Challenger Deep low point of the Mariana Trench - estimated at 10 to 20 kilometers, vs. Challenger Deep’s 10.4 kilometers.
Alternatively, the Kola Superdeep Borehole SG-3 has a depth of over 12.2 kilometers, also deeper than Challenger Deep.
At more than 4,000 km (2,500 mi) long, 200 km (120 mi) wide and up to 7 km (23,000 ft) deep, Valles Marineris is the largest canyon in the Solar System.
Uranus’s moon Miranda has features called coronae, at least one of which has a depth probably exceeding the Challenger Deep low point of the Mariana Trench - estimated at 10 to 20 kilometers, vs. Challenger Deep’s 10.4 kilometers.
Alternatively, the Kola Superdeep Borehole SG-3 has a depth of over 12.2 kilometers, also deeper than Challenger Deep.
That’s… Pretty deep.
But I think we also need total volume.
Wikipedia, re: Valles Marineris on Mars: