Footwear for July layover trip

I am having a footwear dilemma! I am travelling through France this July and doing a 2 night layover at the end of the trip in Iceland in mid-July.

We arrive in the morning and have a plan to explore Reykjavik that day. Then next day we’ve booked the Secret Lagoon and Golden Circle tour with Bustravel Iceland. We fly out the next day.

I have no clue what shoes to bring! We are trying to pack as lightly as possible with travel backpacks so packing hiking shoes would take up a lot of valuable real estate. Tennis shoes are our plan for France but I’m not sure if they’ll be enough if we’re just doing one of those bus tours.

Any help appreciated!