A three-week trip to Vietnam, Cambodia, and Thailand can be an amazing adventure, allowing you to explore the rich cultures, beautiful landscapes, and historical sites in these countries. Here’s a suggested itinerary:

Week 1: Vietnam Day 1-3: Hanoi, Vietnam

• Explore the Old Quarter of Hanoi.
• Visit the Hoan Kiem Lake and Ngoc Son Temple.
• Discover the Ho Chi Minh Mausoleum and One Pillar Pagoda.
• Try Vietnamese street food and visit local markets.

Day 4-6: Halong Bay

• Take a cruise in Halong Bay and enjoy the stunning limestone karsts.
• Try kayaking and explore caves in the area.
• Relax on the beautiful beaches of Cat Ba Island.

Day 7-10: Hoi An, Vietnam

• Explore the charming ancient town of Hoi An.
• Visit Japanese Covered Bridge, Hoi An Old House, and Phuc Kien Assembly Hall.
• Enjoy local cuisine and get tailor-made clothing.

Week 2: Cambodia Day 11-13: Siem Reap, Cambodia

• Explore the Angkor Archaeological Park, including Angkor Wat, Bayon, and Ta Prohm.
• Visit the Angkor National Museum to learn more about Khmer history.
• Experience the vibrant night markets in Siem Reap.

Day 14-16: Phnom Penh, Cambodia

• Explore the Royal Palace and Silver Pagoda.
• Visit the Tuol Sleng Genocide Museum and Killing Fields.
• Take a sunset cruise on the Mekong River.

Week 3: Thailand Day 17-19: Bangkok, Thailand

• Explore the Grand Palace and Wat Pho.
• Take a boat ride along the Chao Phraya River.
• Visit the bustling markets and street food stalls.
• Explore the vibrant nightlife in areas like Khao San Road.

Day 20-22: Chiang Mai, Thailand

• Visit temples like Wat Phra Singh and Wat Phra That Doi Suthep.
• Explore the Old City and its markets.
• Take a day trip to an elephant sanctuary or go trekking in the nearby mountains.
• Enjoy a traditional Thai cooking class.

This itinerary provides a good balance of cultural experiences, historical sites, natural beauty, and relaxation time. However, feel free to adjust it based on your interests and travel pace. Make sure to check visa requirements and any COVID-19 related travel restrictions before your trip, as they may change over time. Enjoy your journey through Southeast Asia!