Unfortunately, we did not have such an opportunity. During the day, because of the bright sun, dunes don't look so beautiful.
The main entertainment in Huacachina is a tour on a special off-road vehicle through the desert and riding on boards from sand dunes (sandboarding). The board can be rented on the spot, but it's not easy to ride without own vehicle. So it makes sense to take a tour for $12-15 (board if included).
Most non-athletic tourists eventually end up riding the sandboard like a sled, face-down on their stomach. This allows for a very simple, and very rapid (sometimes dangerously so) descent of the dunes.
The area around the lake is beautiful and full of restaurants.
Getting there: Huacachina Oasis is located near the city of Ica. Find here bus timetable to / from Ica. Taxi to Huacachina from Ica cost $3-4. Also pay attention to Peru Hop, it is the tourist buses that stop in many places, and you can catch any of them. They go straight into the oasis. For information, check their website: http://www.peruhop.com.