Saylor Academy is not a physical institution, but an online collection of free and open access courses. Their mission is to offer learning free of charge. It's an ideal site for anyone who wants to study a subject in depth, without the expense of enrolling in a university or college. Following these courses means a long-term commitment, but if you really want to learn in detail then a Saylor course is what you're looking for. It may take hundreds of hours, so is only for those who have plenty of spare time or who are in no hurry to complete the course. However, you can take each section at your own pace, so it's flexible enough to fit around your other commitments.