I am spending a week next month (mid March) in Switzerland and will have an 8 day unlimited Swiss rail pass. Beyond the obvious well known/ tourist runs that all the guidebooks mention (e.g., Glacier Express, Belle Epoque, Jungfraujoch) does anyone have any suggestions for fun and interesting train rides worth trying, and why? My schedule is basically wide open, with the only real caveat that I plan on being back in Zurich at the end of the day.