For the runners there is a special tariff offer Vlak+. This is a 3-day return ticket, which is displayed at the station Karlovy Vary. As part of this special offer, the passenger is offered a 25% discount on the return fare. For a return trip free of charge, you have to stamp the ticket at the Czech Railways – České dráhy stand (if the ticket is not stamped, the passenger will pay the difference between the discounted price and the fare to prove entitlement). More info here.