The one- and half-day tours offer new shore-based experiences led by National Geographic-trained guides.
The seven cruise tours are available to book now.
The tours are available across all itineraries that call at Athens, Rhodes and Dubrovnik.
They include the history of the Olympic Games in Athens, oyster farming in Dubrovnik and the ‘Blutopia’ marine biology experience in Rhodes.
All National Geographic day tours meet the Global Sustainable Tourism Council criteria, and every trip booked helps support the global nonprofit National Geographic Society.
Lee Haslett, chief commercial officer at Celestyal, said: “These new cruise tours are the perfect addition to Celestyal’s on-shore experiences.”
“They showcase the rich cultural and natural heritage of each destination, while also contributing to sustainable tourism practices.”
