Works, typically installations, that totally envelop the viewer, often involving constructed environments and multi-sensory experiences. Artists have explored numerous forms of immersion since the development of installation art in the 1960s. Brazilian artist Hélio Oiticica's Tropicália (1967) folded viewers into an environment resembling the country's favelas, while Venezuelan Jesús Rafael Soto's Penetrables (1967-97) employed Op Art experiments to create abstract sculptures that can be walked through. Artists such as James Turrell and Doug Wheeler use the effects of light to create immersive environments. Carsten Höller's works often involve perception-altering experiences, while Olafur Eliasson's The weather project (2003) simulated the appearance of the sun and of cloud formations in London's Tate Modern museum. More recently, artists have used immersion as a means of exploring virtual reality, as in Ryan Trecartin's video installations involving built environments.