`defense against the dark arts classroom,

The Defense Against the Dark Arts classroom is old but huge. If you move aside all the chairs and tables, you can form a space large enough for an entire class to practice a spell - possibly a Boggart banishing spell. It is also filled with various strange looking apparatus that looks like they have been there for near a century.

Remember,"Your defence must therefore be as flexible and inventive as Arts you seek to undo"- Severus Snape.