You could define arthouse cinema as an "I know it when I see it" type of thing, but if more detail is needed, films definable as "arthouse"tend to be unconventional, potentially niche, usually very personal/singular, and also challenging. Arthouse movies can achieve some level of popularity if they speak to enough people, but such films rarely come close to feeling like blockbusters, and are most easily recommendable to viewers who want to experience something different.
Arthouse cinema naturally gets quite strange and surreal at times, with bold visuals, distinct views of the world, and uncompromisingly unique visions on the part of the directors. These aspects of the whole arthouse genre/movement make fantasy a genre that can be combined with an arthouse flavor naturally quite well, with the following films – ranked from good to great – representing arthouse fantasy cinema at its best and most striking.
Taken from Collider's list.