IGS into Lugano in Switzerland was a blast, especially if followed by a visual circle-to-land.

The River visual in DCA is not hard, but you cannot let things get out of hand. Configure early, don't fly too fast, go around Rosslyn at 1000 feet or so and you are golden.

It is fun, but challenging if the wind is strong from the west. Still, not hard and frankly, if someone can't do it then they are not really a pilot, because all it is is a series of turns while descending - basic back-to-the-basics flying.

The Harbor Visual in PWM is cool too, as mentioned.