Imotski

Imotski's claim to fame is two of the world's deepest sinkholes, Crveno jezero (Red Lake) and Modro jezero (Blue Lake). 

​The clifftop above the Crveno jezero (Red Lake) sinkhole reaches to 522m above sea level. (The UK's highest village sits at 463m). That's a pine forest at the top. The surface of the water is at 281m above sea level. That makes the cliffs up to 241m high. The bottom of the sinkhole is 6m below sea level, but it could go deeper - nobody's all that sure. To cap it all, there are no railings around the edge...