From Lisbon
Bus or Train
Train
If you arrive at Humberto Delgado Airport, you can take the subway to Oriente (red line) where you can catch a train to Coimbra (Coimbra-B station).
You can check the timetables at:
Bus
If you arrive at Humberto Delgado Airport, you can take the subway to Jardim Zoológico (you'll have to change from the red line to the blue line at S. Sebastião) and at Sete Rios Bus and Train Station you can catch a bus to Coimbra.
You can check the timetables at:
https://www.rede-expressos.pt/horarios.aspx
From Oporto
Train
Train:
If you arrive at Francisco Sá Carneiro Airport you can take the subway to Porto Campanhã (purple line) where you can catch a train that will take you to Coimbra-B station
You can check the timetables at:

30% off your train ticket
- Only on "Intercidades" and "Regional/IR"
- Trip to and from Coimbra
- Only for participants carrying a registration proof provided by the organization when buying the tickets
- Valid between the 5th and the 11th of September
- refundable
- Revalidable in the same period of time of the discount
- Not cumulative with other discounts or promotions
- Sales channel: CP ticket shops or in transit (only when the station doesn't have a ticket shop).