What are the longest time controls used in chess tournaments?

I realised I've no idea. Players have time to get up and walk around, use the 'confessional' booth, etc but is it like a 60min game or a 8 hour game or what?

For most FIDE events for the first 40 moves each player has 90 minutes. After the 40th move they each get 30 minutes added to their clock and also from that point each move gains 30 seconds. I know some recent ones deviated (which is how Carlsen lost to Topolov earlier this year) but I haven't kept track so I don't know what they used for Sinquefield for example.

Anyway, it can be written like this:
40/90 SD/30+30
Where "SD" means sudden death i.e. the rest of the game. 

A 60 move game may last ~4.5 hours. It's not only that they have time to take a break, you should take breaks to keep your head clear and conserve energy.

So am I wrong thinking we get games lasting days? Maybe in the past?

Of course, a GM doesn't need to be sitting at the board to consider the game. They could walk somewhere nice and relaxing :)

Yes, some games lasted multiple days in the past. Adjournments they called them. The final move of the day wasn't played, it was written down, sealed in an envelop, and given to the director to be opened the next day. Then both players (and their teams if they had them) would spend all night (sometimes) analyzing the position. AFAIK the main reason this stopped was after computers became very strong, so it wasn't practical anymore.

Amateurs sometimes faced adjudications... if the game was going too long one or a few people would decide who was winning (or if it was a draw) and the they would end the game with their decision... sometimes the adjudicator(s) were weaker than the players and got it wrong!

In our local team matches we play the old 2 hrs for 40 moves followed by 1 hr for all remaininig moves. That's 6 hrs maximum.

At a weekend tournament with 5 games (one on friday evenings, two on saturdays and sundays) the time control is shorter, e. g. 2 hrs for 40 moves followed by half an hour for all remaining moves. Between the two games on one day there is something like half an hour lunch break.

Enough time to walk around in the tournament hall, smoke a cigarette outside, go to toilet or get something to drink or eat when your opponent thinks about his move. But there are guys who walk around everytime when the opponent thinks and there are guys who stand up only a very few times during a game. Find out what`s best for you!

I think some more days long games (expect adjudications) where in the 19th century before chess clocks where used. In the first world championship match between Steinitz an Zukertort in 1886 they played this time control:

"The match was to use the same chess clock as 3 years earlier and the time limit was determined as 30 moves in 2 hours, followed by another 15 moves in each subsequent hour."

I'll have to go look but I thought the standard was for the increment to be from move 1.