Museum passes seem like a great deal since you get one ticket for multiple sites, but they have plenty of drawbacks. They may not cover everything you want to see, and can be more expensive than just buying tickets for the sights you want to visit individually, online, before your trip. It's worth it to do your homework in advance. Image from cobacco.
In many major cities, especially in Europe, you can buy passes that cover entry to multiple (often five or more) museums and other sites. That's great if you're going to those places, but even if you are, the maths may not add up. Look up how much the spots you want to go to cost individually, then compare that to the cost of the pass plus any extra tickets you'd have to buy. Ingrid K. Williams, over at the New York Times, gives an example using Amsterdam:
Entrance to most of the area's museums — which are all within easy walking distance — is included in the I amsterdam City Card, available for 24 hours (47 euros, about $57), 48 hours (57 euros, about $69) or 72 hours (67 euros, about $81). Those prices aren't low, although the card includes other perks, including a canal cruise, use of public transportation and discounts on bike rentals and other attractions like the Heineken Experience. Two top museums, the Anne Frank House (admission, 9 euros) and the Rijksmuseum (17.50 euros), do not accept the card, though the latter does offer a 2.50-euro discount to cardholders.
One of the benefits of these passes is that you can usually get them in advance, so you don't wait in line just to buy tickets, then wait in line again to get in. Luckily, lots of museums let you buy your tickets online in advance too, so you can walk right in when you get there — you don't need to shell out for a tourist pass for that perk anymore. If you have the time and interest to take advantage of what these kinds of passes have to offer (like a canal cruise in Amsterdam), then go for it. But if you only want to focus on a few sites, buying tickets on their own can save you money.
Are European Museum Passes Worth the Money? [New York Times]