Sure! Here are some travel tips for your visit to Jeju, Geoje and Yeosu:

Best Time to Visit:
The best time to visit these areas is during the Spring (April to June) when the cherry blossoms bloom and weather is pleasant. However, if you prefer less crowd, Autumn (September to November) can also be considered as it offers a beautiful ambiance with autumn foliage.

Route and Accessibility:
Jeju Island can be reached via a domestic flight from Seoul or by a ferry from the mainland. For Geoje and Yeosu, you can take the KTX (Fast Train) or bus from Seoul.

Altitude and Acclimatization:
Altitude shouldn't be a concern as these areas are coastal cities.

Accommodation and Booking:
It's always advisable to book the accommodation in advance to avoid any last-minute glitches. There are a range of options available as per your budget from luxury hotels, resorts to guesthouses, and homestays.

Clothing and Essentials:
Packing should reflect the season of your visit. So, in spring, casual light clothing is ideal with comfortable walking shoes. Always have a raincoat or umbrella and a hat as weather can be unpredictable. Do not forget your sunblock.

Health and Safety:
Stay hydrated and apply sunblock regularly to protect from sunburn. It's quite safe, but usual travel cautions apply. If you have any food allergies, be clear to mention it as seafood is a staple in these areas.

Local Etiquette and Respect:
South Koreans appreciate if visitors follow local etiquette which includes bowing when you meet someone, using proper titles, and taking off your shoes when entering someone's home. Respectful behavior at religious sites like temples is expected.

These areas are known for spectacular beaches, scenic beauty, and delicious seafood. Enjoy your trip and explore these less-traveled gems of South Korea!