I love the idea of the underground tunnel.

It's a lovely looking place an your photos bring it to life.

I am not familiar with your problem plant, so looked it up. It seems to grow in a wide variety of areas, so I wonder why it refuses to grow for you? I found an article on growing them, here is the link, maybe they have some useful scrap of info to help.

https://www.gardenersworld.com/how-to/grow-plants/pittosporum-tenuifolium/

the photos of Pupper Jack are adorable, of course. Meow like a pirate is priceless. Love those paintings.