<p>I don’t think you can just show up and sit in on Harvard classes. You probably have to get the permission of individual instructors and get the okay from the Admissions office. I would call Harvard Admissions and ask them about sitting in on classes.</p>
<p>The subway (the T’) does not go to Tufts, but you catch a bus from Harvard Square to Tufts. </p>
<p>You could probably do tours of Harvard and Tufts in one day, but fitting in BC the same day is going to be difficult because of transportation issues. I suppose you could take a cab and start at 9:00am at Harvard, hit Tufts around 1pm and BC around 4:00pm, but you need to check all three schools for tour schedules (you can find them on-line) as campus tours and information sessions probably overlap.</p>