Does anyone know of a service that will provide private car transportation (or other alternative, with luggage) between Lisbon and Porto but with stops on the way to see a couple of towns that are interesting? The train is quick and cheap but our group of three thinks it might be fun to combine the trip between cities with some sightseeing. Assume we don't need guides in Lisbon or Porto, just between the cities. Thanks!
If you can’t find such a service then rent a car and drive yourselves. A good guide book will give you the information you need to choose where to stop, etc.
To be clear, we have decided we don't want to drive. But I have found some tour companies that provide the service so unless you know of a specific tour you recommend or a driver, no need to respond.
I'm a relative newcomer to Portugal. I'm planning my own independent trip and have familiarized myself with the train and bus schedules, and I'm doing something similar on my way BACK to Lisbon over a few days with a couple of detours off the main route.
Some in-between towns might lend themselves to using either bus or train on a one-day journey. Others will not. You don't mention which towns, but based on what I've seen... if COIMBRA is on your list of interesting towns - and an interesting town it is, IMO - I'd say that's quite doable, whether by bus or train. I was there years ago and am not stopping there this trip, but the schedules look ample and generally favorable for a 5-6-hour stopover using either trains or buses. The Rede-Expressos bus drops you near the center of Coimbra. Their bus fares run around €6 for each trip ( Lisbon > Coimbra and Coimbra - Porto) for a date one month from now. The trains are a bit faster and there should be lockers there for your bags, but they drop you a bit further out and cost a bit more.
Luggage storage is possible with Bounce, perhaps others: