DENVER - Activist groups say the converted warehouse poses a threat to civil liberties. The city maintains the facility is needed in case of mass arrests during the Democratic National Convention.

The makeshift holding center, dubbed "Gitmo on the Platte" by activists, is located on city-owned property near Steele Street and 38th Avenue. Newly-installed security cameras guard the exterior, chain-link fences and barbed wire form cells inside.

"We feel the city should be ashamed of this secret prison they've set up," said Re-create '68 organizer Glenn Spagnuolo.

City defends 'secret jail' built for DNC