Thirty years ago this month, activists — many fighting for their lives — took to the streets of downtown Chicago in one of the biggest AIDS demonstrations in history. When you cross a battleground and read a plaque commemorating the fallen and the brave, you start to believe you can feel the history in your bones. But what about the unmarked battleground, the one that the next day resumes its role as a city street, an office window, an intersection? April 20 to 23 marks the 30th anniversary of the National AIDS Action for Healthcare, a weekend of gatherings and rallies that culminated in a massive protest in downtown Chicago — one of the largest AIDS demonstrations ever held.