One good example is the Marines Canyon that runs through a huge part of Mars. It's 4000 km long, which is twice as long as the Japanese archipelago. The width reaches 700 km in some places, the and it is 7 km deep. The Grand Canyon is just 30 km wide and 2 km deep. It's so big, you won't even realize you're in a canyon even if you're standing in it!
And of course there's Mt.Olympus, the highest mountain in the Solar System. That's right, the Solar System. It's 25,000meters high and( Mt.Everest is 8848m)-get this- 700 km wide.
Why are structures on Mars so big? I think one reason for it is Mars' weak gravity. It doesn't easily topple high mountains, and also helps them get larger because the force pulling objects down isn't as strong as it is on Earth.