You are right that curves is the way to increase detail at certain brightness levels. The steepness of the line dictates contrast (and hence detail). You only have so much "height" to play with so making the line steeper in one place (e.g. the shadows) means it must be shallower elsewhere. If you're careful you can make the line shallow in an unimportant area (such as where the histogram shows few values, usually at either end) and so get the contrast you need where you need it.

The above used global adjustment (ones that affect the whole image) and is therefore always going to be a compromise (contrast in the shadows means less contrast in the midtones etc.) There is another option, and that is local adjustments. This way you can alter the contrast in certain spatial areas of the image without affecting the others, giving you maximum contrast and detail overall. This is how tonemapping works, which is responsible for the "HDR look". You can get this effect with a single exposure, just Google for "single image HDR". Alternatively you can get a similar effect with the "fill light" slider in Abobe Camera Raw or Lightroom. Finally you can do it old school by masking off the dark areas in Photoshop and altering the contrast with levels/curves.