Madame Tussaud's wax museum is the fairly predictable tourist trap in the Peak Tower, the mall at the terminus of the tram ride at the top of the hill.  In addition to buying tickets at the museum, you can buy tickets at the foot of the hill when you guy your tram tickets.  Buying the combination pack will allow you to cut the long line so it might well be worth it.  In any case, you get what you expect - wax figures you can pose next to, including the venerable James Bond figure for free photo opportunities.