I ended up in the Botanist because as I walked into the garden after passing the Obscura café I noticed a set of stalls selling locally made arts and crafts. As I walked along the row of stalls I ended up in a tunnel under the road in which there were more stalls, a DJ with a desk made of the front of a lorry, and an open space filled with more stalls and shops. I had a chat with one of the sellers who noticed me admiring a carved finger and fingernail about 35 cm tall on a rotating display stand. He said he had admired it for some time and when he got the chance he bought it. He went on to say that the reason it is on a rotating stand is that even he had not noticed how finely carved it was on the underside of the the finger tip. We chatted briefly and I expressed surprise that I hadn't noticed this place on previous visits to Bournemouth and he explained that the tunnel and the rooms had only recently been reopened after being disused for many years.
It turns out it's under Bobby's which I presume used to be a department store. Now it has a cosmetics and beauty products shop on the ground floor, some co-working places on the next two and the Botanist on the top