Main lessons or unit studies are a great way to dive into a subject area. You can focus on a single subject (main lesson) or you can do the tradition unit study approach in which all subjects are intertwined into the unit study which focuses on one area (say plants or animals or the human body) while addressing the other subject areas in an organic way.
We have made our unit studies an extension Waldorf main lessons, focusing on one subject area while daily lessons in math and grammar run parallel to the main lesson.
Memorable lesson: Food!! Roman meal and Ancient Egypt Meal.