There's always something playful about the annual Serpentine Pavilion designs. These temporary structures, making their appearance for a few months every summer on the grounds of London's Kensington Gardens, have an inherent sense of discovery and mischievousness about them. As structures, they are conceived to serve a functional role (a park's meeting and resting space), but they are also follies designed to inspire and excite, freed from some building constraints by their transient nature. This year's offering by Spanish architecture practice SelgasCano – headed by José Selgas and Lucía Cano – is no exception. 

Awash with colour, it's probably even bolder and brighter than Jean Nouvel's brilliant red 2010 edition; the low pavilion's amorphous shape is like nothing the park has seen before. Eye-catching and photogenic, it brings to mind a sprawling, colourful caterpillar, or the retro-sci-fi set of an old episode of Doctor Who

Up close, the structure feels transparent and light – almost too light at times, its surface gently moving in the opening day's light wind. Its thin skin, made out of panels of translucent, multi-coloured fluorine-based polymer (ETFE) 'woven through and wrapped like webbing', covers several steel-framed tunnels that invite you to explore its core. The architects say their inspiration came not only from the site and context, but also from the London Underground tunnel system; it therefore features a number of entrances (and exits) and 'secret' corridors between layers, for free, yet somehow structured circulation. A cafe sits at its heart, offering ice creams and refreshments courtesy of Fortnum & Mason.   

Colour and transparency are frequent elements in the architects' work. Their own office, tucked away in the woods outside Madrid, is partly clad in clear glass, uniting the workspace and nature, while their Merida Factory in Spain and the offices of collaborative workspace Second Home in London bear the practice's signature colours and bold shapes. For the Serpentine, visitor experience defined SelgasCano's approach. 'We sought a way to allow the public to experience architecture through simple elements,' they say. 'Structure, light, transparency, shadows, lightness, form, sensitivity, change surprise, colour and materials.' 

In many ways, the unveiling is a landmark one. It certainly marks the start of the British high summer season, but with this year's completed structure, the gallery is also celebrating the hugely popular scheme's 15th year. (It is, the gallery explains, one of the top-ten most visited architectural and design exhibitions in the world). It also signifies the closing of this year's month-long London Festival of Architecture; the pavilion's opening weekend is the festival's very last. 

Finally, it completes a series of playful shows, currently ongoing at various London venues – the Hayward's Carsten Höller slides, RIBA's Brutalist Playground installation... even this year's RA Summer Exhibition looks into ideas of landscape and outdoors explorations in its architecture room, curated by Ian Ritchie. 

This is just the beginning for the pavilion's four month lifespan. A connected series of talks and events are planned for the duration, while the Serpentine has also launched a brand new initiative around it – Build Your Own Pavilion: Young Architects Competition – a digital platform for young people to submit their own pavilion designs. Winners will be selected at the end of the summer.

TAGS: SERPENTINE GALLERIES