Flamenco Beach is located on Culebra Island, which is about 10 miles east of the east coast of Puerto Rico. I believe that Culebra and Vieques Islands are called the Spanish Virgin Islands (since the US and British Virgin Islands are in the same neighborhood).
First things first - how to get to Flamenco Beach: You can take a ferry or fly out of Fajardo, Puerto Rico (about 30 miles east of San Juan). When we went over to Culebra we took a puddle jumper plane flight - wooden bench seats (with seat belts!), a dog, and the pilot walked out of the airport bar into the plane! The flight only took about 15 minutes and featured a dive bomber approach to the Culebra runway. Once we landed on Culebra Island, in the City of Culebra, we took one of many taxis that show up at the airport to greet arriving planes.
From the airport it is just a 10 minute drive over a couple of low hills to an unreal beach! By the way, on the way back, the plane was full, so we took the ferry back to Fajardo. This was a fraction of the price, but took 2 hours to get back - but, you are looking at the Caribbean the whole time, so it is not unpleasant!
Flamenco Beach is simply put VERY NICE! The sand is almost pure white and incredibly soft. The beach is very wide and very flat - finding a good spot is as easy as sitting down. The water clarity is just silly - you can walk out to your neck, look down and see your toes perfectly clear!
We were there in the summer, so there was not any north side swells out in the Atlantic - because of this and the shape of the bay, the water was glass. In the winter, much like Hawaii, the north facing beaches can get some action. Being out in the water was like being in a huge, perfect, sand-bottomed swimming pool - just crazy!
There are only two options at Flamenco Beach to spend the night - one is the Flamenco Beach Villas (Google search) at east end of the beach and a public campground at the west end of the beach. We stayed at the Villas, which were very basic, but worked. Initially, we had some issues because we got booked into the main building or lodge in a first floor room, which was really a basement room - very poor. After some Spanglish by me and another manager who knew a touch of English, we got relocated to one of the bungalows (Villas is a bit generous).
If you are staying at Flamenco Beach, make sure to bring your food and water, because the little beach bar/snack shack at the Villas has unpredictable hours. Most of the local tourists, bring over their supplies, but you can stop in Culebra to stock up.
On this side of Culebra Island, the only thing to do is the beach - it is an early to bed and early to rise type of arrangement. Very family oriented and mellow - not party central.
The reason it is mid-week paradise, is because of the proximity to Puerto Rico; all the San Juaneros jump over on the weekend. Flamenco Beach and Culebra Island get very full on the weekend with all the city folks from Puerto Rico getting away to the beaches. During our stay at Flemenco, we only had 10 other people on the entire stretch of beach and when we did a little impromptu hiking, we did not see anyone else.
On the way out of Culebra Island, because the flights were full, we took the ferry. The ride was mellow and inexpensive, but we left 45 minutes late. It was a Friday afternoon when we departed, and the incoming ferry was PACKED with tourists - they were unloading pets, coolers, fishing poles, beach volleyball equipment, just everything - even with using two exit ramps, it took over an hour to empty the ferry! When we departed, it was only us and about 5 other people.
If you want to make a quick escape from Puerto Rico and the crowded cities, especially on the east side of Puerto Rico, then Flamenco Beach is the mid-week ticket. For simple paradise on the beach, you can't beat it!