We also used Lisbon Riders for our visit in October based on recommendations here at the Forum. I corresponded before the visit with Manuel and Tania Costa was our guide for two 1/2 to 3/4s day tours: the first an an overall survey of Lisbon and environs, the second to Sintra and the Pena Palace. I found all the Lisbon Riders colleagues (they are a true collective) very pleasant, personable, knowledgable, and very conversant in English. We were especially impressed and pleased with Tania- she is just a great person (and very knowledgable, etc etc....)When I left my computer in the security line in Lisbon airport, she went out and retrieved it and shipped it back to me: I KNOW that wasn't in the job description! Anyway, Lisbon Riders is a great choice and I know you wouldn't be disappointed. They have a number of 1/2 and full day tours organized. 1/2 day for Sintra and the Palace is just about right.