Croatia is a member of the EU, but not part of the Schengen zone. Depending on which country you are travelling from/through, you will need to check whether you require a multiple-entry Schengen visa at the respective diplomatic mission or consular office in your country of residence. EU citizens can enter Croatia with a valid ID or passport. For specific visa requirements for other countries, please click here.
The hotel can support your application with all the documents that need to be presented from the hotel side, such as a reservation confirmation and/or letter of warranty, depending on the purpose of your travel and what kind of visa you are applying for.
Should you need any further guidance, our team at firstname.lastname@example.org will be happy to assist you with finding all relevant information.