The enormous and ornate brick tower you can see here was used to store water in order to get enough pressure (thanks to gravity) to provide water on demand to taps in London houses: a very novel idea in the 1820s! The enormous (three stories high) Cornish steam engines drew water, "fresh" from the Thames, up from reservoirs under the main building. One of them is still working but not to provide water straight from the Thames any more thank goodness. You can also see a giant old beam from a water pumping engine, tadpoles in the little pond in Spring and on weekends you're very likely to see the Museum's little steam engine passing next to the garden.
Anyway, on with the cache details... You are looking for a camo-bison hanging on a hook. We put a silver trinket butterfly inside for the lucky FTF. Please bring your own pen.
It's easy to find using the hint so no need to clamber around in the shrubbery. If the car park is full, be vigilant of neighbouring parking restrictions. It's also only 5 mins walk from Kew Bridge overground station.
This cache has been placed with kind permission of the Staff at the London Museum of Water and Steam.