On a recent visit to Portugal I visited Chaves in the northern area of Tras os Montes (behind the mountains). Chaves is an ancient city in the valley of the Tamega River.
While there I crossed the Roman bridge that was built by the Roman Emperor Trajan about 100 B.C. At one end of the bridge there are several restauurants. I had lunch at one and I sat eating my lunch overlooking the Tamega.
This is the authentic historic section of the city or "The old town". There are many old homes and buildings. There is a fort and castle keep. As I sat there I could just imagine the city as it was in Roman times.
This is a beautiful valley. A peaceful stop while traveling.
Heading north from Lisbon (or Porto) you take the new highway toward Vila Real and then follow the signs to Chaves.
There are several inns and hotels, The Forte de Sao Francisco is a wonderful hotel in the old fort.