Parking on the river front is $8.00 for all day for the Gateway Arch Park grounds and for the other riverfront attractions like the Mississippi boat cruises and the helicopter tours. To get to the parking lot you need to take Chouteau Ave. to Leonor K Sullivan Blvd. and turn left. This will lead you to the parking kiosk.

Here is the Google Map for parking. This parking lot is right on the riverfront so there isn’t a lot of walking involved. I do believe this is the closest parking option available. Please remember don’t go anywhere downtown alone so bring someone with you if you decide to go. Stay safe!
If you prefer to have someone else park your car, then you can choose the valet parking option. With valet parking, a Carnival representative will park your car for you. This option is more convenient than self-parking, but it is typically more expensive.
Thanks for giving detailed information on parking cruises. This will really help me a lot.