Should work in KDE version 5.3.1 but gives error: ''Could not load file 'https://www.socsci.ru.nl/labbooking/ics/room/B.00.56/ultimo.ics'.''
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Korganizer -> right click calendar area -> Add Calendar... -> ICal Calendar File
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Should work in KDE version 5.3.1 but gives error: ''Could not load file 'https://www.socsci.ru.nl/labbooking/ics/room/B.00.56/ultimo.ics'.'' Loading a downloaded version does work.