Absolutely! Visiting Athens, Delphi, and Thessaloníki is like stepping into the eons-old history of Greece. Here are some valuable tips for your travel:

Best Time to Visit:
Spring (April to June) and fall (September and October) are considered the best times to visit. Temperatures are milder, and the tourist crowd generally thins out.

Route and Accessibility:
Arrive in Athens first, which is well-connected globally. From Athens, you can take a direct bus or a train to Thessaloniki, the journey takes about four to five hours. For visiting Delphi from Athens or Thessaloniki, taking a guided day trip can be the most convenient method.

Altitude and Acclimatization:
Athens, Delphi, and Thessaloniki are situated at low altitudes, so you won't require specific acclimatization. However, stay hydrated, especially if you're visiting in the summer.

Accommodation and Booking:
From luxury accommodation to economy lodging, you will find plenty of options. It is recommended to book your accommodations well in advance to get your desired options, especially during peak seasons.

Clothing and Essentials:
Pack light yet comfortable clothing. Don't forget a hat, sunglasses, and good sunblock. Good walking shoes are essential as the cities feature numerous archaeological sites. Also, keep a photocopied document of your passport and visas as back up.

Health and Safety:
Greece is quite safe for tourists. But stay vigilant against potential pickpockets in crowded tourist areas. Carry necessary medicines and stay hydrated.

Local Etiquette and Respect:
Greeks are traditionally hospitable. Acknowledging their customs and traditions makes them feel respected. Dress modestly when visiting Orthodox churches and monasteries. Try learning a few basic Greek phrases like Efharisto (Thank You), which might prove useful.