“OpenLearn aims to break the barriers to education by reaching millions of learners around the world, providing free educational resources and inviting all to sample courses that our registered students take – for free!”
What more could you want, credibility and no fee :)
They have a huge range of courses covering almost every subject area I can think of. They are to be fair sometimes taken from previous versions of full price courses; yet for all that they are still really useful. A free certificate of participation appears to come with most of them too.
And the humungous tortoise? A course on evolution, so Darwin – Galapagos – giant tortoises 😊