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When based in Lisbon take a day trip, first see Queluz Palace then head onto Sintra, which is just 1 hour by train.
A nice place for a day or two (especially in warmer weather) is Estoril along the coast on the way to Porto.
After reaching Porto and visiting the city and some great local wineries, loop back down to Evora on your way back to Lisbon.
We spent 9 or 10 days following the above itinerary and found the pace manageable.