Tripadvisor's 2021 Travelers' Choice of the Best Things to Do, which listed the 15 activities, took into account the quality, quantity and recency of reviews and opinions submitted by travelers on the U.S. travel website over a 12-month period.

The tour, which costs from $79 per person, takes visitors from Hanoi to Tam Coc – Bich Dong, part of UNESCO heritage site Trang An Landscape Complex in Ninh Binh, home to the ancient capital of Hoa Lu during the reign of the Dinh Dynasty (968-980).

The sightseeing ticket for Tam Coc (Three grottoes) costs VND120,000 ($5) per person, with the only way to explore its beauty being a two-hour boat tour down the Ngo Dong River through golden paddy rice fields and limestone caves.

Around four kilometers from Tam Coc is another enthralling spectacle, Hang Mua (Dancing Cave), which looks like a large overturned bell with a width of 800 meters (2,624 feet) at the foot of Mount Mua.

Tripadvisor recommended that visitors should climb up the 500 winding stone steps leading to the peak that looks a bit like the Great Wall in China and cycle to Bich Dong Pagoda, which was built in 1428 and is hidden amid natural caves and majestic mountains.

Once overlooked by tourists, Ninh Binh, around 60 kilometers to the south of Hanoi, has seen its profile rise on the global tourism map since the Hollywood blockbuster "Kong: Skull Island" was shot there in 2016.

Ziplining above forests in New Zealand was ranked the world's best nature and hiking activity, followed by a kayak tour to emerald cave in Nevada.