A network can be analyzed by means of many graph theoretical parameters. In
the context of networks analysis, closeness is a structural metric that
evaluates a node's significance inside a network. A cactus is a connected graph
in which any block is either a cut edge or a cycle. This paper analyzes the
closeness of cacti, we determine the unique graph that minimizes the closeness
over all cacti with fixed numbers of vertices and cycles, which solves an open
problem proposed by Poklukar \& \v{Z}erovnik [Fundam. Inform. 167 (2019)
219--234]