The treasure hunt in the ice is a great sensory play, circulating in many blogs, for example here or here. It is a beautiful summer activity …
It has many features in common with the Montessori proposals, especially with regard to the hand-eye coordination and the development of fine motor skills. The game could also be combined with illustrated cards to match object-color, or with boards for classifying large – medium – small, or light-heavy, etc …
In a “competitive” version it can be played with a larger block, with a group of children. Children play in turn, and the player who gets the most treasures is the winner… but I do not like competition 
I have done so: to make more interesting the block I frozen the objects in successive layers to form multiple levels.
Then I prepared the table using a cutting board and a tray on a towel, a jar of water (if the child is too much trouble to break the ice can serve), various tools (for hammering, chiselling and engrave) and an empty container (alternatively charts referred to above):
