By default it is not possible to include the calendar provided by TUMonline the system of the technical university munich into Google Calendar.
The problem is, that Google Calendar only accepts files with the suffix .ics. I wrote a script that takes a TUMonline calendar link and converts it, that it is usable by Google. If you use this link, you will be redirected to your calendar.
You can either use the version hosted by me or download the source code (licenced under the EUPL) and host the script yourself. You only need a Apache server with mod_rewrite enabled.
Here is the script: http://phynformatik.de/calendar/index.php
And: If you think it is usefull. You have the possibility to flattr it again!