MB2 133a: Idol Worshipper's Spices and Mixtures of Spices (217:5-8) Making a Bracha at the Site of a Miracle (218:1)

When is/isn't a bracha made on the spices of an idolater? What if an aroma is partly from a prohibited item or an item on which it's not appropriate to make a bracha?

The bracha made when visiting the site where a miracle happened to our ancestors. What are examples?