The 0 Euro note is a 'specialty' of Europe.
A paper note with a value of 0 is perhaps unique to the European Union. In terms of security features to combat counterfeiting, it is identical to other 'real' denomination notes: featuring watermarks, UV ink, holograms, or microprinting...

They are fully authorized by the European Central Bank, and without the identifier of '0', they could easily be mistaken for other real Euro notes such as the 5 Euro, 20 Euro...
So what are these 0 Euro notes and why do they exist?
The Euro is a unique type of currency as it is not solely the currency of a single nation, but rather the common currency of a region comprising many different countries - the European Union.
Despite the cultural, geographical, and historical diversity of the countries in the region, Euro banknotes are rather mundane with only 6 official denominations: 5, 10, 20, 50, 100, 200 Euros. Prior to 2013, there was also a 500 Euro note, but it was discontinued in the second issuance.

Furthermore, to avoid favoritism by featuring one country on a banknote while excluding others, the decorative images and symbols on these 6 official banknotes are all... fictitious.
This choice may seem peculiar as in typical countries, banknotes feature prominent figures and iconic landmarks. However, it is the fairest and most reasonable choice for such a diverse region like the EU.
They cannot print hundreds of different versions of banknotes, each featuring a landmark from a different country, as it would confuse tourists and even EU citizens. Moreover, such a choice would pose an immense threat of counterfeiting.
Hence, the 0 Euro note is created solely as a souvenir item to promote European images and figures without affecting the official banknotes used in economic transactions.

The 0 Euro note is printed for tourism promotion purposes.
Its origin dates back to France in 2015 when Richard Faille, the creator of popular souvenir items made from currency in France, decided to introduce the 0 Euro coin to promote tourism. These banknotes are printed by a private subcontracted facility and they share many features with real Euros except for being marked as '0', and are verified to ensure they cannot circulate as a legitimate financial currency.
The front side of all 0 Euro notes is identical, featuring white zeros followed by the Euro symbol to denote zero financial value. Then (from left to right) are depictions of the Brandenburg Gate, Big Ben, Eiffel Tower, Colosseum, Sagrada Familia, Manneken Pis, and the Mona Lisa - iconic landmarks of the continent.

The front side of the 0 Euro note.
Initially created for tourism and promotion, this type of 0 Euro currency quickly became a kind of 'encyclopedia' about Europe and a rich, fascinating collection item for collectors.
Interesting facts about the 0 Euro note
For promotional and collectible purposes, it's not surprising that since its inception, the 0 Euro note has had thousands of different versions, with each country having its own special editions.
A YouTuber named Chris diligently collected 0 Euro banknotes from various European countries. In France, notes featuring the Arc de Triomphe are sold at the very tourist spots they promote. Additionally, two notes featuring the Sacred Heart Basilica and the Eiffel Tower are special as they are made of polymer rather than paper like regular Euros.

The 0 Euro note featuring the Arc de Triomphe. The distinguishing feature in the top right corner is a view of the Eiffel Tower from above.
Another interesting feature is that the watermark and hologram on 0 Euro notes all depict the Eiffel Tower from an aerial perspective.
The rarest 0 Euro note?
For collectors, rare banknotes always hold a curious allure, and the 0 Euro note, created for entertainment and pure collecting purposes, is no exception. The rarest edition of the 0 Euro note must be the one featuring the Marineland aquarium in France, depicting two dolphins leaping out of the water.

The 0 Euro note is considered the rarest today.
In 2015, shortly after the release of this currency, Marineland aquarium suffered a severe flood, resulting in the loss of many marine creatures. However, another significant loss was the printing machine for the aforementioned 0 Euro notes, hence no more Marineland notes have been produced since that flood.
According to Chris, the number of dolphin-themed 0 Euro notes is currently very scarce, thus its market price in the collecting world has skyrocketed like a rocket.
England also has its own 0 Euro note.
Another interesting fact is that despite never officially adopting the Euro and still using banknotes featuring Queen Elizabeth II, England has its own 0 Euro note from its time within the European Union.

Some landmarks featured on England's 0 Euro note include Big Ben, Tower Bridge, the London Eye, Buckingham Palace, and even the famous Titanic ship.
Besides the UK, which was once an EU member, some other European countries possess their own 0 Euro notes despite not being part of the European Union, such as Iceland, Norway, Russia... There are also some EU member states that do not use the official Euro banknotes but have these special commemorative notes, like Poland, the Czech Republic, Sweden...
Source: Banknoteworld, compilation