Sure! Sri Lanka is often called the pearl of the Indian Ocean, and Jaffna, Mannar, and Trincomalee are some of its hidden treasures.

Best Time to Visit:
Jaffna, Mannar, and Trincomalee are located in Sri Lanka's Dry Zone. The ideal time to visit is from February to April when the weather is hot and dry. November through February can also be a good time to go.

Route and Accessibility:
All these places are well-connected to each other through train, bus, and road. From Colombo, you can either drive or take a train to reach Jaffna. Mannar is accessible from Jaffna via road and from Trincomalee via a combination of train and taxi.

Altitude and Acclimatization:
These places lie at relatively low elevations with Jaffna and Mannar located close to sea level and Trincomalee at an elevation of approximately 13 meters. Hence, altitude sickness is not an issue.

Accommodation and Booking:
There are plenty of Hotels, lodges, and Airbnb’s available. Do your research, read reviews, and book in advance as the accommodations can get filled quickly during the tourist season.

Clothing and Essentials:
Carry light, breathable clothing and a hat for protection against the sun during day tours. A good sunscreen and insect repellent are also a must. Pack a sturdy pair of shoes if you plan to explore on foot.

Health and Safety:
Ensure you’re up to date with routine vaccinations. Most importantly Hepatitis A and Typhoid as these can be contracted through contaminated food or water in Sri Lanka.

Local Etiquette and Respect:
Sri Lankan culture is rooted in hospitality and respect. Dress conservative especially in religious sites. Also, respect the local customs and traditions. It would be beneficial to learn a few basic phrases in Tamil or Sinhalese, as it can greatly help in interactions with the locals.