If you really mean that you wish to get to the Lighthouse at Cabo St. Vicente, you should be aware that in winter there is only one bus a day on week days that serves this location. As there is no accommodation, if taking the bus it means that you would have to walk the 5 to 6 kms back to Sagres the nearest town. You may be able to rent a bicycle in Sagres and visit Cabo St. Vicente that way.
This bus is as follows:
Lagos Cabo S.Vicente 10:30 11:25 Mondays to Fridays only.
On this basis, if you are intended making a return trip from Granada, and Cabo St. Vicente is your final destination, a rental car would probably be a good option.
According to Google Maps, the distance is 562 km and will take about about 6 hours each way. I have driven all this route myself and it is motorway all the way to Lagos 40 kms from Cabo St. Vicente - there is a good road from Lagos to Sagres and Cabo St. Vicente. The only potential problem can be bottlemecks on the ring road around Seville.
See this link for a map:
http://maps.google.com/maps?f=d&saddr=Granada,+Spain&daddr=Cape+St+Vincent+-+SW+Portugal&hl=en&geocode=%3BCbs3T9TiCub8FUPaNAIdBLd2_yFjIe6EuYKFRQ&mra=pe&mrcr=0&sll=34.452218,5.493164&sspn=16.814361,37.749023&ie=UTF8&t=h&z=7
If you intend using public transport, the only feasible means is by bus.
This will involve three buses:
Granada - Seville
You would need to get a bus from Granada to Seville Plaza das Armas Bus Station.
www.alsa.es operate from Granada to Seville Est. Prado but then you would need to get a local bus from there to Seville Plaza das Armas.
Buses from Seville to Lagos.
Seville Plaza das Armas - Lagos (Algarve)
Dept: Seville 07:30 Arr Lagos 12:00 Daily
Dept: Seville 16:15 Arr Lagos 20:45 Daily
With the second service you would have to spend the night in Lagos and then continue to Sagres/Cabo St. Vicente the next day. Similiarly, neither of the two buses connects with the only service to Cabo S.Vicente as indicated above. You would need to spend the night in Lagos or Sagres.
Lagos - Sagres - Cabo St. Vicente.
The first bus would connect with the following and later buses to Sagres.
Lagos Sagres 12:40 13:35 Daily
Lagos Sagres 13:35 14:40 Weekdays/Saturdays.
There are about 11 buses per day from Lagos to Sagres. Less at weekends.
A final thought. You might want to stay in Lagos and rent a scooter for the day and ride out to Cabo S.Vicente.
You could try:
Luis of Sidecar 32 in Torraltinha,Lagos is one.
He can be contacted via the following address.
Side Car 32 - Motociclos de Aluguer, Lda.
R. St Casa Misericórdia
8600-621 LAGOS
email: filipe_bolota@hotmail.com
Tel: 282798383
He can deliver a bike to you in town at the Luzcar Office behind the Repsol Garage on the main Avenida.
