The Horniman Museum and Gardens in south London today celebrates the opening of its Centenary Extension. But while it has doubled its viewing capacity, it has lost none of its character.

To describe the Horniman Museum and Gardens as an organically grown hodge-podge collection of collections would be the highest form of compliment, in keeping with the ethos of the establishment. The exterior sets the scene, with Britain’s first Alaskan totem pole, carved in the 1980s, Art Nouveau architecture with Arts and Crafts flourishes, formal gardens and a brand new 21st-century annexe, preparing the visitor for the wildly curious assortment of objects inside.

The Centenary Extension forms a new entrance and creates room for three new galleries, an education centre and a hands-on unit with almost 4,000 objects, from Indian puppets to stuffed alligators.

The permanent galleries contain spectacular specimens across the museum’s three areas of specialisation - ethnography, natural history and musical instruments - and the new education centre provide an opportunity for schools to explore objects in the context of history, science and society in greater detail.

“Most of the hands-on objects are contemporary items which can be used as a way to introduce relevance before the historical learning begins,” says Carolyn Roberts, head of education at the Horniman.

The museum’s collections were originally displayed in the home of founder and philanthropist Frederick Horniman. He and his family opened their doors to the public, but the house became overcrowded with curios. In 1901, the original building - designed by architect Charles Harrison Townsend, responsible for the Whitechapel Art Gallery - was erected as a free museum for “recreation, instruction and enjoyment” in Forest Hill, where it stands today. Adjacent to the museum are 16 acres of gardens. As well as the centenary and music galleries, the African Worlds gallery, the Natural History gallery and the aquarium there is a new temporary exhibition hall.

While all the items on display are extraordinary, some of the objects are more memorable for their unmistakable testament to humanity’s creative drive in its extreme forms. The Spanish Inquisition torture chair was bought by Frederick Horniman for pound;200 in the late 1800s. It was taken out of the display in the 1980s amid doubts of its authenticity, despite its 1676 date stamp. Further investigation revealed that the gruesome parts - such as the horrifying headpiece, belt and back pole - were genuine Spanish tools of torture but not originally part of the chair.

Unmissable in the African Worlds gallery is the rotating display of a very colourful Ijele. From the Igbo people of Nigeria, at around 6m tall and 3.5m across it is Africa’s largest form of mask. This is the only one of its kind in the UK - only two others are on display outside of Africa.

The walrus in the Natural History gallery owes its bloated state to Victorian taxidermists who overstuffed the poor animal because they had never seen one before.

The first exhibition in the temporary gallery is Monster Creepy Crawlies, which runs until the end of October.

Horniman Museum and Gardens, 100 London Road, London SE23 3PQTel: 020 8699 1872 ext 157www.horniman.ac.uk