Glaciated regions are characterized by the presence of U-shaped valleys. A U-shaped valley is formed by the erosional activity of a glacier moving through a landscape. As a glacier advances, it slowly erodes the valley floor and walls, creating a distinct U-shaped cross-section. The glacier has a strong downward force due to its weight, which allows it to erode the landscape more extensively than other erosional processes like rivers.

In contrast, V-shaped valleys are typically formed by the erosional activity of rivers. Rivers have a more gentle erosional force compared to glaciers, resulting in a V-shaped cross-section with steep walls and a narrow, V-shaped floor.

Sand dunes, on the other hand, are formed by wind action and are not directly associated with glaciated regions. Stalactites are mineral formations that hang from the ceiling of caves and are formed by the deposition of minerals through water dripping from the cave roof.

Therefore, the correct option is 2 - U-shaped valley, as it is the characteristic feature of glaciated regions.