Serena, Ray, Serene and I went to Carlsbad Caverns National Park and White Sands National Monument over Thanksgiving break in 2009.
The caves were our first stop on this trip after flying into El Paso. A few weeks before leaving, we decided that it might be a good idea to reserve some guided cave tours beforehand, but most of the interesting cave tours were already full. We got 2 spots in the more interesting lower caves (which Serena and Ray went on), and two other less interesting short walks in the left hand tunnel, and Kings Palace. By the time we had finished walking through the natural entrance and a circuit around the Big Room, I was feeling quite caved out and didn't enjoy the Kings Palance as much as I should have.
Lake Lucero is part of the White Sands National Monument but is located within the White Sands Missile Range. Lake Lucero is pretty cool because it's the source of the white sand (gypsum) that makes up the sand dunes in the national monument. There are lots of gypsum crystals on the ground that crystallize after being washed down from the nearby mountains. They have a trip every month into Lake Lucero (you can't get into the missile range at other times) that coincided with our trip. In White Sands National Monument, we hiked the Alkali Flat trail, which is quite a pleasant walk over the white sand dunes.