Absolutely, I'd be delighted to help you plan your trip to Matara, Galle, and Unawatuna in Sri Lanka!

Best Time to Visit:
The best time to visit these coastal cities in Sri Lanka is from December to April. This is the driest season and temperatures are warm, making it perfect for indulging in beach activities and sightseeing.

Route and Accessibility:
Colombo Bandaranaike International Airport is the main international gateway to Sri Lanka. From the airport, you can get to Matara by taking the Southern Expressway (E01) or by train. After visiting Matara, you can travel northward to Galle and Unawatuna. Trains and buses are frequently available for these routes.

Accommodation and Booking:
All three cities offer a wide variety of accommodations from budget hostels to luxury resorts. It is advised to book your accommodations in advance especially during the peak season (December to April) as they can fill up quickly.

Clothing and Essentials:
You should pack lightweight cotton clothing suitable for warm tropical climate. Don't forget to pack a swimsuit, beach towel, sunblock, and a hat. Also bring travel adapters if your devices don't use Type D or Type G sockets.

Health and Safety:
Make sure you're up-to-date on routine vaccines before your trip. Insect repellent is highly recommended as there can be mosquitoes. Always stay hydrated and protect yourself from the sun. Beware of strong currents when swimming in the sea.

Local Etiquette and Respect:
Sri Lankans are very friendly and respectful. Remember to dress modestly when visiting temples and other holy places. It’s also considered polite to remove your shoes when entering houses or religious sites.