Blue Caves (Greece) - 21
Cueva de los Cristales - 20 - 3 = 17 Huuum, I had not noticed you. I'm sorry, it's a very beautiful place to enjoy, but caves are not poissible like natural wonders in civilization.
Danxia - 21
Delicate Arch - 17
Erta Ale - 21
Great Blue Hole - 21
Guilin Mountains - 21
Iguaçu Falls - 21
Isle of Skye - 20
Kīlauea - 21
Ko Samui - 17
Lake Baikal - 20 + 1 = 21 Very beautiful lake. Sounds great on the map.
Lambert Glacier - 20
Lençóis Maranhenses - 21
Macocha Gorge - 21
Mammoth Cave -13
Mariana Trench - 5
Salar de Uyuni - 20
Serengeti - 14
Underwater Waterfall (Mauritius) - 22
Wadden Sea - 14
White Desert (Egypt) - 21
Cueva de los Cristales - 20 - 3 = 17 Huuum, I had not noticed you. I'm sorry, it's a very beautiful place to enjoy, but caves are not poissible like natural wonders in civilization.
Danxia - 21
Delicate Arch - 17
Erta Ale - 21
Great Blue Hole - 21
Guilin Mountains - 21
Iguaçu Falls - 21
Isle of Skye - 20
Kīlauea - 21
Ko Samui - 17
Lake Baikal - 20 + 1 = 21 Very beautiful lake. Sounds great on the map.
Lambert Glacier - 20
Lençóis Maranhenses - 21
Macocha Gorge - 21
Mammoth Cave -13
Mariana Trench - 5
Salar de Uyuni - 20
Serengeti - 14
Underwater Waterfall (Mauritius) - 22
Wadden Sea - 14
White Desert (Egypt) - 21

It's a great choice for a NW. Trust me, I've been there. 