Whanganui district councillors and residents have been perplexed by the appearance of four bikes on the Whanganui's South Mole.
Currently, there are two full-sized bikes on the mole, with one small child's bike and one larger child's bike placed in front.
According to Horizons Regional Council spokeswoman Kate Ritani, the first bike appeared on the mole a little over a year ago, with the other three appearing over the last few months.
As for the origin of the bikes or who could be behind the installations, Ritani said she did not know.
"They are a bit of a mystery. No one seems to know how they ended up on the South Mole," she said.