“Do you want me to give you a leg up?” my sixteen year old asks. A bit of low-key trespass clearly appeals. The plant-dotted ruins and rain-filled pits are intriguing but we decide to be sensible and stay on the right side of the fence.

This is what remains of the Crystal Palace marine aquarium, built on the fire-damaged north end of the site. When it opened in 1871 it was purportedly the largest of its type in the world with salt water for the tanks brought by train from the sea at Brighton. Historical accounts suggest that Charles Darwin was a regular visitor. While this aquarium was technically innovative it wasn’t a commercial success and closed in the 1890s.

A pair of mallards are swimming through the weed-choked rainwater under crumbling arches. Safe from foxes but not nosy humans, they’re spooked when I hold my camera over the fence to take a picture and fly off shrieking.

Only a mile and a half down the road is the the Horniman Museum aquarium in Forest Hill. Despite its modest size, this is home to Project Coral and “became the first institution globally to successfully induce predictable broadcast coral spawning as well as the first successful in-vitro fertilisation of captive corals in the UK.”

Two extraordinary ground-breaking aquariums in south east London. Beat that!