The apartment is between the 14 and 15km mark on La Manga Strip. 

At the 12km mark you will drive past the entrance to Thomas Maestre harbour and restaurants, keep going over the bridge (13km mark) until you see the Spar supermaket on your left (after 14km). Slow down here, and take the next turning on your left towards the Navemar Nautica boat showroom. The apartment building is directly opposite the Navemar showroom (red star on the map below).