The Marrakech medina is designed to disorient, and the guide question there is less about interpretation than about not being led into a shop.
Iceland is a self-drive country with three specific exceptions, and knowing which they are saves both money and a rental insurance argument.
Kyoto's famous temples are calm at opening and unbearable by eleven, which makes the hour you arrive worth more than any guide.
London's flagship museums are free, which means the tours worth buying are the ones giving access rather than interpretation.
Two Barcelona sites sell out weeks ahead and the rest of the city needs no tickets at all, which is most of what you need to know.
The Louvre needs a strategy rather than a guide, and Versailles needs neither if you get the timing right.
Rome is the one European city where guided access genuinely changes what you see, because half the significant sites are underground or restricted.