NGC 6357: the Lobster

At the heart of the Lobster nebula is a compact cluster of exceptionally hot stars, Pismis 24. The radiation from the cluster ionizes much of the surrounding gas to an unusual extent, giving rise to strong OIII emission (in blue in this Hubble-palette rendition).
The angular size of the nebula is well matched to the field of view of CHI-2, used for this image. I've left the image in a slightly 'softer' state than i might normally choose, but zooming in will still reveal a lot of fine detail.