Train travel from Lisbon to Santiago de Compostela

To my knowledge, there is no train going from Portugal into Spain in that area. I know you can take the train as far as Guimarães with no difficulties. I would imagine you will have to take a bus into Spain. You might look at the website Rome2rio. They are really good at giving all the options for transport.

There is only one train from Portugal to Spain and its from Lisbon to Madrid.

From what I know you can only do Lisbon => Porto (https://www.cp.pt/passageiros/en/), then Porto => Vigo (via Celta Train ==> https://www.cp.pt/passageiros/en/how-to-travel/celta), and finally, Vigo => Santiago de Compostela (look for it at the Renfe website ==> http://www.renfe.com/EN/viajeros/index.html).

This would be a 8 to 9-hour trip, depending on the type of train you pick from Lisbon to Porto, not considering all the waiting time between trains.

You're finding something that surprises many, until they do the research - connections between Spain and Portugal are surprisingly skimpy. There are a very few trains (often at odd hours), there are some buses, and there are flights. And if you rent a car in one country and drop it in another, there's a surcharge, which can be surprisingly high. So, combining Spain and Portugal in one trip can be much harder than one would think. If you have the time, you've been given a route that will work; most likely, you'll want to make some stops on the way.

A good way to get train routes and schedules for most of Europe is the Bahn (German Rail) website http://reiseauskunft.bahn.de/bin/query.exe/en, following Rick's tutorial: http://www.ricksteves.com/travel-tips/transportation/trains/online-schedules. Note that this only has prices for trains that start or end in Germany.

Although it isn't really an unattractive city, Vigo, of all the places I saw in Galicia, is not a place I'd choose to spend extra time. There just didn't seem to be anything special about it. In addition to Santiago de Compostela, I preferred A Coruna and Pontevedra. The small border own of Tui (Spain) is worth an hour or two of wandering, and there are many attractive coastal towns reachable by bus from the larger cities.

If this is a summer trip, be prepared for some coolish, wettish weather in parts of Galicia. Santiago de Compostela is notorious for lack of sunshine.

The train from Lisbon to Porto is fast and efficient.

We took a tour from Porto to Santiago de Compostela that was great. Found it on Viator.