Geological formation, Karst / caves
15 WHS

Aggtelek and Slovak Karst
Alejandro de Humboldt National Park
Carlsbad Caverns
Desembarco del Granma National Park
Gunung Mulu
Ha Long Bay
Lena Pillars
Mammoth Cave
Nahanni National Park
Phong Nha - Ke Bang
Purnululu National Park
Skocjan Caves
South China Karst
Trang An
Tsingy de Bemaraha

See: http://www.worldheritagesite.org/categories/category9.html

14. Y = 7 (inc 2 choices from 3 and 2 as below) N = 7 (including the non chosen!)
Aggtelek and Slovak Karst N? - only one of Aggtelek, Skocjan and Mammoth?
Alejandro de Humboldt National Park N? - either it or Desembarco to represent the Caribbean?
Carlsbad Caverns N?
Desembarco del Granma National Park N? - either it or Alejandro?
Gunung Mulu - Y
Ha Long Bay - Y
Mammoth Cave - N? - only one of Aggtelek, Skocjan and Mammoth?
Nahanni National Park N
Phong Nha - Ke Bang N - only just scraped in on OUV
Purnululu National Park - Y sandstone Karst
Skocjan Caves - N? - only one of Aggtelek, Skocjan and Mammoth?
South China Karst - Y
Trang An - N - not on Geological criteria - it needs consideration as a CL
Tsingy de Bemaraha - Y

As readers of this website may have noticed, this is probably my least favourite category.
Would like to know somewhat more about the differences between these sites. Why is South China Karst a Yes?

"One of 2 great karst areas of the World"
The skocjan selection would major on caves - this on stone forests etc

There is also the "iconic" aspect of Guilin etc.

I think Lena Pillars should be included here.

This is my list

Aggtelek and Slovak Karst
Gunung Mulu National Park
Ha Long Bay
Mammoth Cave
Nahanni National Park
Phong Nha - Ke Bang
South China Karst
Tsingy de Bemaraha
Lena pillars (better suits this catagory)

I would back the following:

Gunung Mulu
Ha Long Bay
South China Karst
Tsingy de Bemarha
Lena Pilars
Mammoth
Phong Nha

This may be one of my favorite categories, since I love caves and karst topography. As such, I have a hard time limiting my choices:

1. Ha Long Bay: Perhaps the most recognized example of karst topography
2. South China Karst: One of the best examples of continental karsts worldwide
3. Carlsbad Caverns*: Excellent and extensive example of a karst cave system
4. Skocjan Caves: This is purely sentimental, since these caves in the Kras Plateau are where the study of karst topography began

*I've been to Mammoth Cave, and while it was notable for its size, I've enjoyed many smaller caves in the US more; I'd rather give the nod to Carlsbad for its impressive formations.

added it!

With the new discovery of Hang Son Doong Cave in Phong Nha Ke Bang NP, the world largest cave. From picture I think it should be on the top list.

http://www.telegraph.co.uk/news/picturegalleries/earth/10914205/In-pictures-Inside-Ha ng-Son-Doong-the-worlds-largest-caves-in-Vietnam.html?frame=2948990

Interesting!

Why not Gunung Mulu National Park or Tsingy de Bemaraha (seems quite iconic)?

= "As of 2009 it has the largest known cave passage cross-section in the world" (according to Wiki)

I think we have another criterium here (next to iconic, unique, worth a journey): the largest/biggest/oldest etc

My selection:
Ha Long Bay
South China Karst
Tsingy
Possibly: Skocjan or Carlsbad

I was being stingy and limiting my choices! Gunung Mulu would also be a great example of a karst cave. The karst pinnacles are also well known, and something I'd like to see, so I certainly wouldn't mind if it makes the cut! I'm not sure Tsingy de Bemaraha offers anything that Gunung Mulu doesn't have; I'd be more inclined to recognize Madagascar for its fauna with Rainforests of the Atsinanana.

Now that Lena Pillars is in this category, I'd also submit that Lena Pillars would be a unique example of a frost-derived karst. The pillars have looked impressive in all the pictures I've seen.