Police said the shower block was parked illegally and the operation to remove it lasted about 50 minutes.
The block was secured overnight and the Wellington City Council would collect it today.
One "civilian car" received minor damage during the removal operation.
Police said they were focused on containing the protest within its perimeter and they would continue to seize any "large infrastructure" protesters tried to bring in if it breached the law or local bylaws.
"These items will not be returned."
About 300 vehicles remained around the protest area and police said they would let those wishing to leave do so, via a one-way exit.
Police understood there were a number of protesters' vehicles trying to leave the occupation, but they were currently being blocked by other protesters, the statement said.
"Police will continue to have a highly visible presence in and around Parliament grounds to reassure local residents, businesses and people in the area throughout the day."