Documenta visitors flock to these works of art

The Parthenon of Books on Friedrichplatz Square in Kassel, the city that hosts the documenta art exhibition every five years, is a crowd-puller. Created by Argentine artist Marta Minujin, it draws attention to the censorship and persecution of writers. Most artworks at the documenta are critical of society, though not always as clearly as this installation.

The Parthenon of Books is an exact replica of the temple on the Acropolis in Athens, a symbolic link between the two documenta venues this year, Athens and Kassel. With as many as 100,000 banned books from all over the globe, the installation is set on a square where the Nazis burned books that didn't fit their ideology.

The Mill of Blood by Mexican artist Antonio Vega Macotela points a finger at the exploitation of labor. This artwork is a replica of a Bolivian mill used to make silver coins in colonial times. Slaves from the Andes had to turn the wheels, and the mill owners made a fortune.

Visitors can try their hand at moving the giant wheels, which is fun for kids and adults alike. Turning the wheels was so popular from day one of the exhibition that the transmission broke and had to be repaired early on.

Ibrahim Mahama's artwork also targets hard labor. With the help of refugees and volunteers in Athens, the Ghanaian sewed together burlap sacks to form a huge blanket for the Torwache building in Kassel. The sacks breathe tales of faraway places and goods like cocoa or coffee beans. Rich countries continue to benefit from poorly-paid raw material suppliers.

The white smoke spiraling from Daniel Knorr's Expiration Movement installation on the Zwehrenturm tower tends to confuse visitors. Since the art exhibtion opened in Athens in April, smoke has billowed from the tower, keeping the fire department busy as concerned citizens often call it in.When the wind blows it to Friedrichsplatz, it is supposed to remind people of the Nazi book burnings.

Iraqi conceptual artist Hiwa K created an artwork that is very popular with visitors: a stack of horizontal earthenware pipes, reminiscent of similar tubes refugees took shelter in when they arrived in the Greek port of Patras. Hiwa K clearly focuses on the current European refugee debate.

Kassel University students furnished the pipes under the artist's scrutiny: a bathroom of sorts, a kitchen, a bar and a library (above). A horizontal perspective was important to Hiwa K. The work is meant to challenge the expectation that up is good and down is dubious.

In 1965, traveling Chilean artists and poets founded the Ciudad Abierta ("Open City") collective which still astonishes visitors with makeshift outdoor construction projects. In Kassel, the collective presents improvised, environmentally-friendly constructions.

"I was a stranger and you took me in," engravings in four languages read on Olu Oguibe's obelisk. The monument symbolizes people in exile. In recognition of his work, the Nigerian-born US artist won the Arnold Bode Award, endowed with 10,000 euros ($11,700). The documenta contemporary art exhibition runs through September 17.