Any trip we plan, the first thing we look for is whether there is a "DK Eyewitness" book. These are fantastic trip-planning books with lots of photos and original artwork drawings of, for example, cutaway views of palaces, churches, etc. They are full color on glossy paper so are fairly heavy books to actually carry, so we often leave them at home. Their (huge) strength is the tourist planning information on history, maps, routes, places, sights, etc. Information on hotels, restaurants, etc. is weaker but that is easy to get from any of the usual paperbacks like Lonely Planet, Steves, Frommer, etc. We usually buy one of them too.
Here ya go:
https://www.amazon.com/DK-Eyewitness-Travel-Guide-Portugal/dp/1465411534