org-caldav can also be used for standalone import of ICS files to Org.
In particular, see org-caldav-import-ics-buffer-to-org to import
iCalendar entries (e.g. from e-mail attachments) directly to your
org-caldav-inbox.
Also, see org-caldav-convert-ics-to-datetree to convert an iCalendar
file into an Org datetree in a separate buffer (use
org-caldav-datetree-treetype to control the style of datetree).