There is a little shopfront in Bethnal Green in London with a desiccated body of a mermaid in the window. This is Viktor Wynd's Last Tuesday Society. In here you can enjoy an absinthe in the bar and pop downstairs to see shrunken heads and sit next to a lioness.
It was voted best bar in London in 2019, and the bar is really fascinating, with interesting artwork on the walls, books on the shelves to browse through, and large numbers of skulls and skeletons looming down from above. They have an extensive range of absinthe, all of which are served in the traditional way, which is an experience worth going for alone (and perhaps followed up with a cocktail with a scorpion on top - it was a bit soggy though, unlike the tasty crunchy scorpions I've had elsewhere..).
Down below the bar is the museum area, which even though it is fairly small in terms of floor space (two rooms, essentially), one could spend hours and hours carefully examining all of the hundreds of exhibits that are crammed in. Some are macabre, some are curious, some are simply amusing.
They also run courses and lectures on various topics. Looking at the website currently shows one on "Masks and death rites of the Bismark Sea".
It probably isn't a place for everybody to visit, and I will state now that the photographs below contain some objects which may offend some people.
And, if you're in London and find this sort of thing interesting, do check out the Horniman Museum in Forest Hill.