' s ▁E ve , ▁ 1 9 9 4 , ▁the ▁found ers ▁of ▁Environment al ▁Enc ro achment — D ave ▁Christ ensen ▁and ▁Mike ▁Smith — al ong ▁with ▁a ▁group ▁of ▁friends , ▁built ▁the ▁first ▁open - to - the - public ▁art ▁play ground ▁environment ▁with ▁a ▁h anging ▁cargo ▁net ▁for ▁clim bing , ▁a ▁zip - line , ▁a ▁revol ving ▁see - s aw , ▁and ▁also ▁a ▁cru de ▁set ▁of ▁drums ▁and ▁bar rel s ▁for ▁providing ▁music . ▁This ▁installation ▁was ▁the ▁start ▁of ▁many ▁gu err illa - style ▁events ▁through ▁the ▁year , ▁including ▁a ▁net ▁and ▁swing ▁h anging ▁under ▁the ▁ 1 8 th ▁Street ▁Bridge ▁over ▁the ▁Chicago ▁River , ▁and ▁a ▁gu err illa ▁play ground ▁on ▁a ▁l ago on ▁island ▁in ▁H umb old t ▁Park ▁( Ch icago ▁park ). ▁More ▁install ations ▁became ▁more ▁elaborate ▁and ▁performance ▁within ▁the ▁installation ▁evol ved . ▁Inter active ▁sculpt ures , ▁as ▁well ▁as ▁the ▁style ▁of ▁net ▁hang ings ▁and ▁zip - line ▁r ides , ▁were ▁a ▁fresh ▁addition ▁to ▁Chicago ' s ▁art ▁and ▁music ▁scene . ▁ ▁Dave ▁Christ ensen ' s ▁" Fre ak ▁Bi ke ", ▁a ▁four - person ▁drum ▁b icy cle , ▁which ▁Smith ▁and ▁Christ ensen ▁sm ugg led ▁onto ▁Navy ▁Pier ▁for ▁that ▁year ' s ▁Art ▁Chicago ▁International ▁Ex position , ▁became ▁another ▁mode ▁of ▁mobile ▁and ▁interactive ▁art . ▁They ▁also