People from North America won't need an adaptor. Europeans need an adaptor. However, the plug-ins are recessed into the wall within a 2 inch circle. So, basic appliances like hairdryers will be fine, but the big plug-ins that are on, say, a battery charger, won't fit within the recess.
To get around this problem, I used an adapter for the skinny versus thick prongs (you know how most plug-ins now have one straight and one wide prong?). It stuck out from the recess in the wall, then I plugged my battery charger into the adapter.