This package adds Czech public holidays to the Emacs calendar.
If you have org-agenda-include-diary set to t, these will be also listed in the org-agenda view.
This package is available on MELPA, just M-x package-install czech-holidays. If you want to install it manually, clone this repository somewhere, add it to load-path, and add (require 'czech-holidays) to .emacs.
Add a call to (czech-holidays-add) somewhere in your .emacs. Note that this must be called before Emacs calendar is loaded.