The botanical garden occupies the land adjacent to the Vordingborg Castle ruins, making use of the old moat and the sheltered ground within the remaining castle walls. Entry is free and the garden is open throughout the day. It is a modest but carefully maintained collection, with roses and perennial beds that are at their best in June and July.
The combination of medieval stonework and cultivated planting is unexpectedly pleasant — you can walk through the garden and into the castle ruins without a clear boundary between the two. Local people use it as a lunchtime park in summer. It adds almost nothing to your time budget if you are already visiting the castle, and it would be a shame to miss it.