To subscribe to the Clustermarket booking calendar on your Android device you will need to do so using Google Calendar on a desktop device:
Install Google calendar on your desktop device
Copy the link from the Clustermarket booking calendar to your desktop calendar,
On your computer, open Google Calendar.
On the left, next to "Other calendars," click Add + > From URL.
Enter the calendar's address.
Click Add calendar. The calendar appears on the left, under "Other calendars."
On your Android phone or tablet, download the Google Calendar app from Google Play.
When you open the app, all of your events will be synced with your computer.
Tip: It might take up to 24 hours for changes to show in your Google Calendar when you link to your Clustermarket booking calendar.