Public buses based in Cobán make frequent runs to Las Verapaces' towns. Transportes Monja Blanca has regular service between Guatemala City and Cobán, passing the Biotopo del Quetzal (the driver will let you off if you ask). Relying on public transportation makes it difficult to visit some of the farther-flung attractions such as Semuc Champey or the caves at Lanquín, but there are plenty of private shuttle services and tour operators that will take you to these sites.
Transportes Monja Blanca. 7952–1536; 7951–1793 in Cobán; 2238–1409 in Guatemala City.