  In this paper we explicitly calculate the analogue of the 't Hooft SU(2)
Yang--Mills instantons on Gibbons--Hawking multi-centered gravitational
instantons which come in two parallel families: the multi-Eguchi--Hanson, or
A_k ALE gravitational instantons and the multi-Taub--NUT, or A_k ALF
gravitational instantons. We calculate their action and find the reducible
ones. Following Kronheimer we also exploit the U(1) invariance of our solutions
and study the corresponding explicit singular SU(2) magnetic monopole solutions
on Euclidean three-space.
