Hello there! That sounds like a fantastic adventure. Here are some detailed travel tips for your visit to Athens, Delphi, and Thessaloníki in Greece.

Best Time to Visit:
The best time to visit Greece is in Spring (April to early-June) and Autumn (September and October). The weather during these periods is usually mild and there are fewer tourists, which makes sightseeing more enjoyable.

Route and Accessibility:
You can reach Athens by direct flights from many international airports. From there, you can travel to Delphi and Thessaloniki via intercity buses or trains. If you want more convenience, consider renting a car.

Accommodation and Booking:
You'll find a range of accommodation options in all three cities, from luxury hotels to budget-friendly hostels. I recommend using reputable websites for booking accommodations. It's best to book in advance, especially if you're travelling in the peak season.

Clothing and Essentials:
The weather in Greece varies by season. Summers can be hot, so lightweight clothing, sunscreen, and a hat are recommended. In Spring or Autumn, pack some light layers and a jacket for cooler evenings. Comfortable walking shoes are essential for exploring the historical sites.

Health and Safety:
Greece is generally safe for tourists. However, in any foreign place, it's wise to stay vigilant, especially in crowded areas. Make sure to have a copy of your travel insurance documents for any medical emergencies. Also, don't forget to keep yourself hydrated.

Local Etiquette and Respect:
Greeks are known for their hospitality. It's respectful to greet locals with a smile and attempt a few basic Greek phrases. Dress modestly when visiting religious sites.