That doesn't sound at all clueless to me! I'm glad you are not offended - I didn't want to diss what you were saying, but school is so embedded in our society that it takes ages to stop thinking that the school system is the custodian of knowledge.
I'd say you are exactly on the right lines. Perhaps you could also do interesting things with the photos when you get home (e.g., if they are digital you can use a photoediting program to modify the images, create a web page or a slide show, etc).
How Children Learn at Home by Alan Thomas and Harriet Pattison is well worth reading - it is about "informal learning". They are researchers from the Instutute of Education (not EHEers) and they conclude that informal learning is at least as efficient as formal learning, at least up to 12-13yo. They also admit that it is not codifiable - by 12-13 all the children they studied were at least equal to their school peers in maths and English, but they could not say how it happened and it happened differently for each child.
The trick is to not be anxious that you cannot see what is happening. A bit like being a gardener at Kew - you have to trust things will grow because if you dig them up every week to check, then you know they won't. Sometimes they don't anyway, but it is not a disaster because something else does (analogy breakdown). For example, if your DS is able to reel off a million facts about transport and LU, does it matter that he has not done a project on the Vikings?
My DD is an expert on the Tudor courts. She has been reading about them since about 10 - now 18 - and had books by David Starkey and Alison Weir for Christmas at 13. She came in the other day with a book on British History from 1700, for research into something she is writing. The point is that she is still interested and is extending her interest because she has her own reason, not because a curriculum advisor thinks that all 10yos need to know about the Victorians, IYSWIM.
Your DS may decide that he wants to start building models of the LU. He may be interested in the story A Subway Named Möbius by A.J. Deutsch (trains disappear because an engineer accidentally builds a train line as a Möbius strip). That leads onto lots of interesting geometry and other maths... You get the idea.