A Friendly Ghost
I lived in a warehouse in East London and in a former life the site had been experimental orchards for a famous gardening family the Loddiges who built the world's first heat hothouse /Greenhouse just around the corner.
I would often hear footsteps on the top stairs and loud bangs on the top floor in the middle of the night, when there was nobody else there, and although I wasn't afraid, I tried to get in touch with the maker of the racket.
In the calm of a a nocturnal meditation I managed to locate the intruder who was a rather pleasant and bumbling old man. It turned out he was the spirit of an old gardener who was still hanging around.
We had been collecting growing cacti at the warehouse for quite some time and had quite an impressive selection of succulent and spiked cactuses dotted around the top floor and he said that he found it fascinating and liked to watch them grow. In his life he had a general dislike of cacti due to their troublesome spines but that wasn't a problem now, he added with a chuckle.