How to play against the Ruy Lopez Berlin defence?

Curious, why do you think Black would be unlikely to have a line prepared against the Four Knights'?  If Black is willing to play 1.e4 e5 2.Nf3 Nc6 surely he has to take 3.Nc3 into account and 3...Nf6 is the number one move.

Also there are Black options aside from the ones you gave.  4...Bb4, 4...Nd4, 4...Bd6 are all valid tries.

I am a little curious to know why you have 1. e4 e5 2. Nf3 Nc6 3. Nc3 Nf6 4. Bb5 Bc5 as the mainline. 4...Bb4 is over three times more common, 4...Nd4 has a name (Rubinstein), chess 365 even has transpositions into the Ruy Lopez old Stenitz defense with 4...d6 occuring more frequently then 4...Bc5.

I wanted to write something but Greencastleblock has written it all. I get four knights roughly once every 4 or 5 berlin games. Personally I play Nd4. This is a game by me on chess.com with the Nd4 line with 3 days thinking time (up until the 13th move everything is explained on Jan Gustaffson excelent dvd series on e5 part 2) 

4...Bd6 is a nice move against the four-knights.

I had ment Bb4. My reasoning is that Nc3 and the four knights in general is less common in the king's pawn opening so black is less likely to know the lines but even if he does white can get a comfortable game. GreenCastleBlock Nd4 leads to a messy exchange and white comes out with the better structure, Bd6 puts the bishop in a funny spot that blocks black's d-pawn, and Bb4 is what is the main line and what I'd ment to say

Actually, Bd6 is a very respectable line that scores extremely well.

First of all, you've clearly not done any study of the ...Bd6 line; it is debatable whether at GM level White can get any advantage at all.  ...Bd6 fits given White's Bb5: White can't physically play Nb5, and if White ever plays Bxc6 then after ..dxc6 Black's Bd6 is perfectly normal.  Given time Black will play ..O-O and ..Re8, this enables ..Bf8 which again is a normal repositioning in a closed Lopez.  White's only attempt at an advantage is to play to open the position with a quick d4, but Black has the resources to handle this.

Secondly, if Black is not prepared for the Four Knights' game, it is his own fault, unless, after 1.e4 e5 2.Nf3 Nc6 3.Nc3 he intends to play a sideline like 3...g6 or 3...f5, and doesn't bother to study 3...Nf6 lines at all.  But if that is the case, why is he playing 3...Nf6 against the Ruy Lopez? I don't get your logic for why this is likely to catch Black off guard.  It sounds like you have heard titled players hawking their opening books using the phrase "which the opponent is unlikely to know" and are parroting them without any reasoning.

Nd4 against the spanish 4 knights is played by: Svidler, Bacrot, Karjakin, Kramnik, Radjabov, Gelfand, Aronian, Timman, Naiditsch, Shirov, Caruana, Giri, Bologan, Kamsky, Grischuk Mamedyarov, Carlsen, Leko and many more top 100 players players 

If they all think it is fine it sure is fine for me !

Did someone try this against Berlin Defense? 1.e4 e5 2.Nf3 Nc6 3.Bb5 Nf6 4.O-O Nxe4 5.d4 Nd6 6.dxe5 Nxb5 and now 7.c4!? I tried this experimental move better than 7.a4 because 7.c4 has a great control at the center and White´s attack is too strong! Analyse it? As White,you can develop Nc3 normally adding pressure at the center.Black will have difficulty in his development.

While the Spanish Four Knights (4.Nc3) or the slow 4.d3 are both "acceptable", best is to go for the slightly favorable endgame line, 4.O-O Nxe4 5.d4 Nd6 6.Bxc6 dxc6 7.dxe5 Nf5 8.Qxd8+ Kxd8 9.Nc3! (Best).

Now how to proceed depends a lot on how Black responds.  Just remember, the cardinal sin is to allow Black to trade off that Dark-Squared Bishop for your c3-Knight.  So in other words, moves like 10.Re1 are TERRIBLE!

White has his pawn on e5, unlike e4 in the Exchange Ruy.  This will virtually force f4 to be played in order to protect it.  But how do you get in the f5-break?  You need to play g4 at some point.  That's what Black's game is all about.  Preventing g4 by White.  The Dark-Squared Bishop has no way of contributing directly to the g4-square.  Therefore, the best thing the DSB can do is trade itself off for a White Knight!  White's Light-Squared Bishop is gone while a Black Knight is gone, so the number of pieces that can control g4 is equal.  If you let Black trade off the DSB for a Knight, he's one-up on you in the battle for g4, and about the absolutely worst that will happen to Black is he will draw.  Trade the DSB for a White Knight, get that pawn to c5 (controling b4 and d4) and block the e-pawn with Be6 (after ...h6 to stop Ng5) and get that Black King then to c6, and White can almost resign.  This is what you must not allow!

For yourself, if you can knock out the LSB with your Knight, and get to a pure Knight ending or Same color Bishop ending, Black's hopes of holding on are bleak.  Also, always be on the lookout for sacrifices of the e-pawn, pushing e6 to open up lines for your DSB.

This actually is a brand new idea- say some sixty years old.

White should be able to equalize after 7.c4 d6, although I am not so certain about the way it can be done. My engine claims Black has a slight advantage, but I never trusted his judgement in openings.

If White wants to avoid the Berlin, the Petroff and all that slghtly annoying stuff, then the 4 knights is a very decent choice. The current trend of obnoxious sideleines is Giri's 1.e4 e5 2.Nf3 Nc6 3.Nc3 Nc6 4.h3!?, swhich may look like a stupid loss of time, yet it was good enough to give him 2,5 points out of 3 against Caruana, Cramnik and Adams.

Anyone have info about the variation with Bg5 that Magnus played in the simul?

This is a brand new line, introduced by Harry Nelson Pillsbury just 120 years ago.

Both 6...Be7 and 6...f6 look good enough for equality, but this does not mean much if you play against Carlsen.

How I normally play as either white or black:

Anybody have thoughts on 4.d4 against the Berlin? (If 4...Nxe4 then 5.dxe5 looks like it transposes to a line of the Two Knights Defence against the Italian or to a sideline after 4.O-O.)

The positions after 4... Nxd4, 4... exd4, 4... Nxe4 5.dxe5 Be7, and 4... Nxe4 5.dxe5 d5 all seem fine to me.

If one wants to get reasonable winning chances against the Berlin without trading queens, there is always 1. e4 e5 2. Nf3 Nc6 3. Bb5 Nf6 4. Qe2!, which is my personal favorite.

Andrew Greet wrote a repertoire book on that. Most excellent author in my opinion.

Thanks TheGreatOogieBoogie. That does look unpleasant for white. But through playing around with the chess.com game explorer, could white avoid that type of position with 5.O-O or 7.Ba4 or something else?

There is a video by Andrew Martin that covers the berlin ("The ABC of the Ruy Lopez). My personal favorite is 5.d3, with a closed game. Black will most likely transpose into 3..a6 lines, with  4.d3. It is pretty good for white.