The problem is simply to find a path around a collection of bridges that crosses each bridge exactly once.
Eulerian paths have interesting properties, both mathematically and computationally.
The islands are in the middle of a river. In our garden the river is represented by the garden. Euler is supposed to have proved that there is no solution when he was working in St. Petersberg. There could only be a solution if every island had an even number of bridges touching it, since one must leave an island the same number of times one arrives at it. Alternatively, exactly two islands can have an odd number of bridges, and these must be the start and finish point of the tour.