How to backup the Android calendar file (is there such a file)?

Does anybody know which files I need to save in order to have a simple backup? Reason for my question is, that my Galaxy Android smartphone lost all calendar data without any interaction. I found tons of apps, tons of sync stuff, but NO simple list of files to save. I do NOT want to save my data remotely on Google. There must be at least one local file (database?) on my phone containing the synced calendar file (on my server, using ICSSync)