The fastest way to reach the National Pantheon is by train. There is a train station right next to this monument and it is called Santa Apolonia. The trains that you need to catch are: AP,IC or IR. You may also use metro blue line or bus lines 712 or 734. All this will take you directly to Pantheon. Pantheon is only 20 minutes from the city center so might even have a nice walk.
