As Congress works in the coming months to reach accord on legislation that would provide billions of dollars to address the National Park System's nearly $12 billion in maintenance work that's been put off for a year or longer, the backlog continues to inch higher and higher. If a funding mechanism is passed, then the National Park Service will have to craft a national priority list of projects that need to be tackled. While that list doesn't exist yet, here's a look at some possible top priorities.