We have done an article on northern monsters before and this one is no less infamous in Nordic folklore.
Nykur is a creature that looks just like an ordinary horse and most often comes in various grey hues. The only difference being that the nykur has his hoofs on backwards. In any other way he appears just like an ordinary horse yet his intentions and actions are that of a horrible monster that people have learned to fear.
The Nykur has been known by many names, Nykur being the most common. It is also simply called water horse or by the names Nennir, Nóni, Vatnaskratti (Water devil) and Kumbur.
One of the distinguishing trades that the nykur is known by is his appearance in and around water. It is most often seen close to lakes and rivers and in some cases the sea. This has been reported in Nordic countries and perhaps even other parts of the worlds. It has even been said that during winter when lakes are frozen over and the explosive sound of breaking ice is heard, that it is the neighing of a Nykur.
The nykur likes to lure unsuspecting people to sit on its back, which it will allow just as a friendly horse would. When the person has climbed on top it will leap into the nearest source of water and drown the helpless victim.
Few details are known of this creature but it is said that to drive one of you only have to say their name as they hate to hear their name. It has also been said that a Nykur can have offspring with horses and the result from such a union is a horse like any horse. Yet it is known that if anyone tries to ride such a horse over a stream or a body of water he will lay down as soon as he feels water upon his chest.
Many areas have been named after this creature. For example in Iceland some have been named for example Nykurtjorn(Nykur pond), Nykurvatn(Nykur Lake), NykurPyttur (Nykur Pit) and many many more.