Forus Chamartín (Centro Deportivo Municipal Chamartín)

Formerly a 50m pool, when they permanently divided it, they took 2½ meters out of the total length. This created two pools, one of 25 meters and the other of 22½ meters.
Locks can be purchased for €4 from a vending machine downstairs prior to entering the locker rooms.
New: Identification is required for access, passport worked well.

Just back from a great swim at this location. Day passes are limited and available only for entry Monday through Thursday from 6 to 9 PM. (I'm not sure if the restriction is applicable year-round or only in summer.) The 50 meter pool was divided into two halves, with a total of sixteen 25 meter lanes. I got in the pool exactly at 6 PM and swam for an hour without sharing my lane.
Bring a towel, toiletries (no soap is provided in showers), and a small lock for the lockers provided (make sure it's a small lock, as a standard lock won't fit through hasp).

The pool is in excellent condition and very clean. Due to its size it's usually possible to have a good swim tho' evenings and lunch times are busiest.

The pool is very nice; water about 79ºF (26ºC) -comfortable, but cool. Mornings are the best times, by 2 PM it starts to get crowded. Unfortunately, in Madrid pools lane discipline is not enforced and it can be difficult to get in a good swim if the pool is crowded.