public static void openCalendar(final Activity activity, final Date date) {
        final Uri.Builder builder = CalendarContract.CONTENT_URI.buildUpon();
        builder.appendPath("time");
        ContentUris.appendId(builder, date.getTime());
        final Intent intent = new Intent(Intent.ACTION_VIEW).setData(builder.build());
        activity.startActivity(intent);
    }
Open the calendar app on a specific date.
main/src/main/java/cgeo/geocaching/utils/CalendarUtils.java