Da Lat topped the most romantic destinations list for Valentine's Day.
"This beautiful land of flowers has fascinated and attracted couples from all walks of life with its peaceful life, picturesque sceneries, and year-round cold weather," the U.S.-based agency stated.
Some activities ideal for couples are taking a swan-shaped boat ride on the iconic Xuan Huong Lake, taking a dip at beautiful waterfalls like Pongour or Prenn or visit Valley of Love.
Hoi An ancient town in central Vietnam came in second on the list. Couples are recommended to stroll around streets full of colorful lanterns or enjoy a cyclo tour or release lanterns onto the Hoai River.
Hoi An also made it into the list of 21 most romantic places in the world as voted by editors of U.K.-based Time Out Magazine.
Da Nang City, which neighbors Hoi An, came in third in the domestic list; described as "all-in-one heaven for couples who like to do it all" by Booking.com.
"Blessed with a variety of natural landscapes like the sea, mountains, rivers, islands, Da Nang will offer couples the opportunity to create different types of beautiful memories all on one trip," it wrote.
Da Nang is famous for long, sandy beaches like My Khe and major tourist attractions like Han River and Golden Bridge.
Sa Pa, a popular tourist town in northern Lao Cai Province famed for rice terraces and cloudy landscapes, secured fourth spot, followed by beach town Nha Trang.
The rest of the top 10 were Phu Quoc, Hanoi, Hue, Mui Ne and Cat Ba Island in the northern Hai Phong City.