Reñaca is your typical beach-side town with tons of highrise apartment buildings and hotels along a beach, but the difference is that they're all built on hills and on the beaches, you can rent lounge chairs, an umbrella, and anything else for the day (or by the hour). It's pretty cool. It's also handy because almost nobody sells beach towels, and the ones that do are surf shops that sell towels by Quiksilver and other brands, and cost about US $50. So, make sure you bring a towel if you go.
We weren't overly impressed with the area, but the beach is wide and sandy, yet crowded. As you can see, the weather wasn't cooperating as much as we had hoped. We had a great lunch at a sushi place there after it got cloudy and too cold to lay out any longer.
Sushi Home Beach was awesome. We were some of the only ones in the place and the staff was really friendly. Our waiter was bilingual but put up with our terrible accents speaking Spanish and walked us through the menu, and gave us excellent recommendations for rolls and side dishes. We started the day off right with some pisco sours (as you do in Chile) and got to work on our rolls.