Which organism built this 2 cm long sandy tube?
This is the nest of a Mud dauber, also known as Mud wasp. This was possibly made by a Black and Yellow Mud dauber based on the following information.

The nest of the black and yellow mud dauber is a simple, one-cell, urn-shaped nest. 1*


As for expecting something coming out of it? I doubt it, as the nests are sealed after depositing an egg.

After building a cell of the nest, the female wasp captures several spiders. The captured prey are stung and paralyzed before being placed in the nest (usually 6-15 per cell), and then a single egg is deposited on the prey within each cell. The wasp then seals the cell with a thick mud plug. 2*
Eventually, the hatching larva will eat the prey and emerge from the nest.