I will have some leather shoes and then some gray Nike's. The Nike's are way more comfortable so I want to do that but I know some cathedrals have specific rules. I know most will make you wear pants instead of shorts but is there anything specific about tennis shoes for cathedrals that I should know?
Thanks for the help.
No.
Some of the friars even wear sandals with their toes hanging out.
Knees and shoulders are the things to keep covered - - sometimes that doesn't matter - - there'll be signs.
I've worn sneakers, hikers, and sandals (not at the same time) into many churches, cathedrals and basilicas (not sure about the differences, even after several years of study) in Italy and lots of other countries and I've never seen anyone checking footwear.
Barefoot might not be okay. I've been tempted by the cold stone floors on hot summer days . . .
Sneakers/tennis shoes will be fine.
@Chani: a basilica is an architecural floorplan style, most European churches after about 300CE use this plan (like Saint Peter's in Rome). A cathedral is the church where the bishop of the diocese presides, regardless of architectural style (in Rome it's Saint John Lateran).
and the root, 'cathedra', is Latin for the ceremonial seat/throne of a bishop
Adding on to Ed's comment, you may find yourself entering a basilica and not a cathedral. As Ed explains a cathedral is the seat of the Bishop. For example, if you visit La Sagrada Famila in Barcelona, it's not a cathedral, it's a minor basilica. The cathedral in Barcelona is elsewhere in the city. Same with the famous church in Assisi. It's a basilica. The main cathedral is farther up the hill. Sneakers or tennis shoes should work in any of them regardless of their description.
