"[3] Some of Sierra's most famous works have involved paying a man to live behind a brick wall for 15 days, paying Iraqi immigrants to wear protective clothing and be coated in hardening polyurethane foam as "free form" sculptures,[4] blocking the entrance of Lisson Gallery with a metal wall on opening night, sealing the entrance of the Spanish Pavilion at the Venice Biennale, only to allow Spanish citizens in to see an exhibition of left over pieces of the previous year's exhibition.
[3] Another of his well-known projects is a room of mud in Hanover, Germany, commemorating the job-creation measure origin of the Maschsee.
In 2006, he provoked controversy with his installation "245 cubic metres", a gas chamber created inside a former synagogue in Pulheim, Germany.
"[3] In 2010 he received Spain's National Award for Plastic Arts but publicly rejected it, claiming his independence from a state which shows "contempt for the mandate to work for the common good".
[7] In explanation of his work, Sierra has said, "What I do is refuse to deny the principles that underlie the creation of an object of luxury: from the watchman who sits next to a Monet for eight hours a day, to the doorman who controls who comes in, to the source of the funds used to buy the collection.