Start with a Vestas V164 (really big) off shore wind turbine. 7MW installed capacity, 105 meter tall tower.
Pick a load factor - I will be generous with 33.3% so P=2.331WM average power output.
Pick a calm period - Europe usually gets five consecutive days of calm each winter. T = 5*24*60*60 = 432000 seconds.
Required energy storage is E = PxT = 10^11 Joules
Pick a height and depth: I will go for H=100 meters high and D=10 meters deep. The density of water is d=1000kg/m^3, and gravity (g) is a little under 10N/kg. The required area A is: A = E/Ddgh = 10000.
Water can be sucked up 10 meters - if you try to go higher, the water rises 10 meters and you get a vacuum above it. My pumped storage V164 has to take its mechanical power to the base of the tower, then pump water up into the 40 Olympic swimming pools supported by a forest of 100 meter tall towers.
In real life, transporting several MW of mechanical power 100 meters is not trivial, and you are better of converting it to electricity and back (75% efficient).