We stopped off in Metropolis after seeing signs for the Largest Superman Statue on the highway. Side note: the signs are very helpful in leading you straight to the attraction, we didn't need to break out the phones or GPS or anything.
The superman statue was a towering figure and a great photo opp. There were also other photo cut-outs to put your head in as Superman and Supergirl. There's a fun little Superman/superhero store across from the statue. The store is connected to the Superman Museum, which there is an entrance fee for.
However long you stay, stopping at the statue is a great place to stretch your legs and snap some sweet pics.