The most popular pilgrim trail after the famous Camino Frances in Spain is the Camino Portugués or Caminho Português in Portugal.

The recently opened and longer route in Portugal is approximately 612 km (380 miles) that starts in Lisbon and passes through stunning unspoiled countryside before arriving in Santiago in Spain. It takes 23-26 days to complete.
Between Lisbon and Santarém, and between Ansião and Porto, this route is coincides with the routes to Fátima being developed by the Centro Nacional de Cultura. It is marked with blue arrows in the direction of Fátima and yellow in the direction of Santiago. Between Santarém and Ansião, pilgrims have a choice between a blue/yellow route via Fátima and a yellow route via Tomar.
Alternatively, one can chose to start further north in the medieval heart of Porto and wind their way up through northern Portugal, cross over the Rio Minho into Spain at Tui, and then continue north to Santiago for a distance of 241 km (150 miles). It takes approximately 10 days to walk this shorter section.
From Porto, there are two routes to Ponte de Lima and on to the border at Valença de Minho, the Central one via Barcelos (126km), and a variant via Braga, called the Caminho Português do Interior (140km).
For an outline of this northern section, visit the website of the Associação dos Amigos do Caminho de Santiago do Norte de Portugal.
For detailed maps, description and photos of the entire route visit the website of the ASOCIACIÓN GALEGA DE AMIGOS DO CAMIÑO DE SANTIAGO
The best English guide of the entire route is, “A Pilgrim's Guide to the Camino Portugués” by John Brierley.
Published by the Findhorn Press, this guide includes detailed maps of the main routes, and descriptions of alterative routes and information about accommodation. It covers the entire route from Lisbon to Oporto (13 stages) and Oporto to Santiago Spain (10 stages). The book is available through Amazon or directly from the publisher Findhorn Press.
Second edition published in 2009
ISBN-10: 1844091570
ISBN-13: 978-1844091577
More information about the guide is at this site.
Between May and June it can be wet and windy, while summer is hot and busy. September and October the weather is most stable and this is considered the most ideal time to walk it. Accommodation is a mixture of pilgrims hostels (least expensive), bed and breakfast, small pensions and quintas (most expensive). There is no or little pilgrim style accommodation from Lisbon to Porto.