What is the biggest puzzle that exists ?

According to Guinness world records, The biggest puzzle exist is a puzzle with 551,232 pieces,

With an overall measurement of 14.85 x 23.20 m (48 ft 8.64 in x 76 ft 1.38 in),

It was solved by 1600 students in Vietnam, It took them 17 hours to complete it.

The page in Guinness world records website