Grade 4 students at J.W. Walker School demonstrated Monday afternoon how they, and fellow students, have been going about building an ice castle as part of their science lesson on structures. The students have spent the past week constructing the wall of about 275 “bricks,” which are made by freezing water in empty milk cartons. Students are asking residents to donate their used cartons, which can be dropped off at the school either empty or already filled with water. They hope to complete the project next month.