How to experience Carnival (Karneval) in Germany?

Basically, there are two different kind of carnival in Germany. The one in the Rhineland, called Rhenish Carnival and the one in the Southern part of Germany, that looks similar to the Carnival in parts of Switzerland and Austria.

The Rhenish Carnival is especially strong in Cologne, Mainz and Düsseldorf. In the Southern region of Germany, the Carnival is also called Fastnacht, Fasnet, or Fasnacht (and a lot of similar names).

In both regions, you can expect the highlight of the Carnival around the weekend before Ash Wednesday, including the days before and after the weekend. Basically in all regions, there are non-stop activities from early Thursday morning until Tuesday 23:59:59. Officially, Carnival start at 11:11 on November 11th, but before the weekend mentioned above, there aren't a lot of activities, expect for the weekends in the new year.

Generally, you can expect a lot of happy drunk people that are wearing funny, weird, humorous costumes. You can also expect so called Guggenmusik, a Carnival marching band. In the Rhenish Carneval they know how to play their instruments, while in the southern regions it is basically noise.

However, I personally prefer the southern version of the Carnival. For me it is more fun and not formal.

Edit

I was asked to elaborate on the difference between the Rhenish and the southern version on the carnival. I'm exaggerating a little bit, but that's my personal opinion:

In the Rhenish version, you experince typically things like "Karnevalssitzungen" and for instance Rosenmontagumzug:

On the other hand, in the southern part and also especially in Austria, Switzerland and Liechtenstein, you can attend Maskenbälle, Monsterkonzerte and Fasnachtsumzüge:

Actually, I also found a video from 2009:

http://www.youtube.com/watch?v=raSxi3142KE

(bounty of 100 rep for everyone who finds my in the video)

Well, I am German and I know what Karneval is.

To tell the truth, if a foreign guest would suggest to visit "Karneval" in Cologne, I would flinch and my face would show a freezing grin.

I despise, detest, loathe Karneval in Cologne. Heartily.

Still tolerable for me is visiting carneval processions. But visiting a "standard carneval" session is like having toothache.

Imagine a bunch of people who are taking themselves very seriously meeting in a room who is constructed by people who know academically what "humor" is. The reason for meeting in this room is showing off your high position in the society. To show that you have "humor" you are wearing cap and bells. Remember Steven Hauk from "Good morning, Vietnam" ? You are now getting "carneval speeches" called "Büttenrede" spiked with dirty jokes which are one magnitude worse than Hauk. But it does not matter because most people are drunk. Drinking no alcohol this is no option for me, so I had to experience it fully alert. My memories of this event occur, if ever, only at at three o clock at night.

Alternative carneval sessions are called "Stunk", but after my traumatic experience I never visited one.

So if you have, ahem, mixed feelings after visiting carneval: You are not alone.