Sure, I’d be happy to help! Here are some travel recommendations for visiting Ioánnina, Párga, and Thessaloníki in Greece:

Best Time to Visit:
Greece is a country that can be visited all year round, but the best time to visit depends on what you want to see and do. The spring (April to June) and autumn (September and October) periods are ideal if you're looking to enjoy mild weather and fewer crowds.

Route and Accessibility:
If you're starting in Athens, take a flight or a bus to Ioánnina, continue by bus to Párga, and then head to Thessaloníki by bus or flight. Rental cars are easily available if you wish to navigate at your own pace.

Altitude and Acclimatization:
Altitude will not be a problem in these areas as they are located close to sea level.

Accommodation and Booking:
There is a range of accommodation options from luxury hotels to budget guesthouses in all these cities. It's recommended to book in advance, especially during the peak holiday season.

Clothing and Essentials:
Pack according to the season. During summer, light, breathable clothing is recommended. Include a good pair of walking shoes, a hat, sunscreen, and sunglasses. Winters can be chilly, so pack layers and a good coat.

Health and Safety:
Ensure that you have travel insurance. Keep alert for pickpockets in busy, tourist areas. As always, basic precautions should be applied, such as not leaving your belongings unattended and keeping an eye on your food and drink.

Local Etiquette and Respect:
In Greece, it's appreciated if visitors attempt a few words or phrases in Greek. It's also a custom to dress modestly while visiting Orthodox churches, so for women, it's recommended to have a scarf to cover your head and for men, long pants are preferred. Remember to enjoy the local culture and traditions.