The tallest peak in the solar system is Olympus Mons of Mars, three times taller than Mount Everest. But it's not as easy to say what the second tallest mountain is...but it might be found in the unlikeliest of places.
We've had fun with imagining climbing the solar system's peaks before, but we found out firsthand that it isn't easy coming up with an exact list of the highest peaks in the solar system. We know that Olympus Mons has an elevation of about 15 miles, and then other super-tall peaks on Venus and Jupiter's moon Io top out at about 7 miles. That's all still comfortably taller than Everest's 5.5 miles, but it's hard to tell which peak takes the prize for the solar system's second-tallest.