You may travel by bus to Covilhã or Belmonte, the nearest cities to Manteigas served by bus, from either Lisbon, Porto, Faro or Guarda.

Departure times and itineraries depend on whether you are travelling on a weekday or weekend.

Ticketing and booking: http://www.rede-expressos.pt

Lisbon - How to get from the airport to the bus terminal?

Taxi or underground (Metro) are the best options. The terminal is at Sete Rios close to the Lisbon Zoo (Jardim Zoológico). Here is the Lisbon's Metro network map:

Porto - How to get from the airport to the bus terminal?

Underground (Metro) is the best option. The terminal is close to the Bolhão stop. Here is the Porto's Metro network map:

By Train

You may travel by train to Covilhã or Guarda, the nearest cities to Manteigas served by train, from either Lisbon, Porto or Faro.

Departure times and itineraries depend on whether you are travelling on a weekday or weekend. We strongly advise to use the "IC" service.

Ticketing and booking: http://www.cp.pt/passageiros/en/

Lisbon - How to get from the airport to the train station?

Underground (Metro) is the best option. The train station is at the Oriente stop. Here is the Lisbon's Metro network map:

Porto - How to get from the airport to the train station?

Underground (Metro) is the best option. The terminal is at the Campanhã stop. Here is the Porto's Metro network map:

You can fly to one of the three Portuguese airports or to Madrid - Barajas (Spain).
Distances to Manteigas are approximately 300km from Lisbon (LIS); 300km from Porto (OPO); 500km from Faro (FAO) and 420km from Madrid (MAD).

Those are all of the international airline companies which fly to these airports.