In the case of Spain, many long distance roads are no longer safe for pedestrians as there are cars on them now. Madrid to Milan would be a suicide missions in current day.
This is a Street View link to Via Augusta, one of the oldest roads between Spain and Italy (8 to 2 BC). It’s not walkable anymore. There isn’t an alternative footpath. You might hike on the beach and climb the rocks in between but that is significantly harder than cobblestones.
What you call sandals the Romans called boots. Their boots were open on the top but still heavily soled. This suited their climate and kept the foot cool and dry.
These were hob nailed thick soles leather boots where the uppers were a series of adjustable straps. I don't think there's anything modern that's comparable.
The closest in terms of function would probably be the jungle boot, where the uppers have drains and fabric air circulation panels built in to keep the foot cooler and dryer.
These boots were designed to allow the wearer to walk long distances without discomfort in the Mediterranean climate of the Roman empire