recommended "must see" that tours do not offer

What are you interested in? Museums, architecture ancient sites? Tours usually all hit the main "must see" sites, others would be things that specifically interest you.

Donna

Go to the Lido when in Venice but walk next to the beach towards the end of the island. The places you will pass are fascinating.You should enjoy walking the Dorsoduro dection, across the Grand Canal from the St Mark's area.
In Rome, almost always overlooked is Ostia Antica-- easily gotten to by Metro.Also near Rome is Via Appia, which is a quiet and gorgeous walk in bucolic surroundings. Rick's Italy book features a how-to of getting there. As we remember, it involves a train and then a bus.
Firenze's Piazzale Michelangelo is unforgettably lovely. Dunno if tours take you there but it shouldnt be missed. For slice of life by locals , check out places like Affitecamere Freda-Lucia on Via Zenobi.

Most tours seem to only spend 1 or 2 days in each of these cities. For me, the "must see" is the city itself. Getting away from the crowds and wandering. Grabbing a snack at a little cafe, sitting on a quiet piazza watching families play with the dog, weaving in and out of little shops and talking to shopowners, etc. It seems like most tours don't offer the chance to really stay in one city for a few days to really get a feel for it. Most tours also don't offer staying in teeny-tiny B&Bs. I have stayed in establishments with 7 or fewer rooms in all 3 of those cities, and I think that greatly enhanced my experiences of each.