Obtaining a PhD with an original work I was wondering if there still exist universities (in the US or in Europe) where one can obtain a PhD in Philosophy by only presenting an original and well-developed work around a subject or an author.
Yes. Many UK Universities have it in their regulations to permit the award of a degree by prior publication.

However, that does not mean you can just submit your publication and expect to receive a doctorate! The regulations permit the university to recognise someone, usually already associated with the institution, who has made some publication of academic merit made by a non-academic that has received some form of public praise to be rewarded and recognised by the university for their work. This is distinct from a degree honoris causa which may be awarded to honour the person who has done some deed that is not  a publication of equivalent worth to a thesis.

An example, of my personal knowledge, is someone who spent their life studying local flora and published a significant catalogue of plants as an amature botanist. The academic nature of the work was recognised by the University with the award of a Phd by prior publication. I have also known it happen to a local playwright for a lifes work.