When I visit London I always try to go to the mineral hall at the Natural History Museum. It is truly fascinating. Not just the exhibits but the way they are displayed, as if trapped in time in the 1960's. I dread the day the displays themselves are updated. The other good thing about it is, there are never more than half a dozen people in there (why?) So, if you need to think, write or meditate it's actually pretty much guaranteed to be quiet. Occasionally, you get the odd person who doesn't look at anything but flies through taking photos, seems a very odd way of enjoying the exhibits....later, on a screen. Hello! They are right there in front of you!!