Your best bet for parking is probably the covered parking garage at Station Square which is a short walk from the incline. If the weather is inclement, or you feel like shopping, cross the street from the parking garage and walk through the Station Square Commerce Court where you can find restaurants for any taste, Pittsburgh sports regalia of every kind, ice cream, unique artwork and more. Go all the way to the end of the converted train terminal and exit at the intersection of Carson Street and the Smithfield Street Bridge.
Click here to pop a Google Map of the Station Square Parking Garage in a new window.
Pro Tip: If you're planning on starting at the upper station of the Mon Incline, the Pittsburgh Parking Authority lot on Shiloh Street has free parking on Sundays. Make sure and check out the excellent Grandview Bakery across the street to fuel up with some sweet treats!