As others seem to be promoting their sims I thought it would be ok for me to do so as well.
I am a Historical Consultant for movies, tv and museums in RL and am obsessed with history, I just love it.
During my travels in SL I missed realistic, authentic historical roleplay sims, there were a few that looked very nice but generally the sims and the roleplaying was a little too romantic.
Buildings were very pretty and people enjoyed portraying rich ladies and gentlemen.
I missed the narrow streets, the muck in the dark corners, the poor people, etc.
I decided to build my own sim; The 1920s Berlin Project.
The theme is, as the title suggests, 1920s Berlin.
This old city has always had a very interesting and exciting history but in the 1920s, shortly after the horrendous First World War, it entered an era like no other.
The world changed dramatically, progress brought Jazz, flappers, zeppelins, movies, radios, short dresses (shock horror!), more freedom, liberty, etc..
BUT in Berlin all these new things spread like a virus and were enjoyed in more extreme ways then any other country.
Freedom, drug use, prostitution, tolerance, liberation, modern art, it all happened.
Berlin was the place to be!
And no prohibition... 
It was a golden age of music, entertainment, art... but also a dangerous and scary time of unrest, frustrations and extreme politics.
Riots in the streets, Communists, Nazi's, Anarchists... poverty, addictions, crime...
People were dancing, but they were dancing on top of a vulcano.
Our 1920s Berlin Project sim is a roleplay sim that tries to recreate a little bit of this vibrant history.
With the limited options SL offers us we have rebuild some of the famous parts of the city center that you can explore as a tourist.
You arrive at our small 'Teleportplatz' where you can shop at some of the best vintage shops in SL, you can buy great vintage clothing but of course there are also plenty of excellent freebies, even a free 1920s car!
Once you've changed into a 1920s outfit (one of our rules) you can enter the train and travel to Berlin.
There is too much to see to mention, cinema, shops, offices, buildings, Unter Den Linden, the only 1:1 scale reproduction of the Brandenburg gate in SL, bathhouse (with pool), the famous Hotel Adlon, but also the darker side of the city with poverty and sinful delights
We are a very strong community, some of our tenants have lived with us for almost 2 years, often you have to wait for weeks or even months before apartments become available.
Roleplay often reenacts nothing more then daily life in 1929, but sometimes it gets dramatic with murder, intrige, riots and mysteries.
We have many jobs and vacancies for anyone who wants to make a living in our city.
Realism, authenticity and history is what we aim for.
We have some great events, EVERY day at 2 pm slt we have a little Happy Hour at the Tanzlokal 'Der Keller' where you can drink, chat and dance to our original 1920s (ad free) music stream.
But we also have church services, theatre shows, cabaret, dance balls, etc, etc.
Sunday the 10th we have Relaxed Rules day, for 24 hours we forget about our strict dress code and will allow people in modern clothing and non-realistic avatars.
Great excuse to come and have a look if you don't like changing outfit or avatar.
And on any day you can take an airship tour over the city and see it from above without changing your outfit, you can find out more about this at the Teleport Station.
More about our sim;
http://www.1920sberlin.com/
Here our flickr Photo group;
http://www.flickr.com/groups/20sberlin/
And finally, you can find our sim here;
http://slurl.com/secondlife/1920s%20Berlin/236/232
Mmmmh what kind of advice?
All I can say is; just do it
What I generally do is think up a little background story for the person I am while visiting the sim.
In 1920s Berlin I am a Dutch woman who married a German man who died during the war, left behind as a war widow I managed to scrape some money together and open a bar.
Ask yourself who you are, why you are in Berlin and what you want to do there.
Visit the Happy Hours and try and meet the other people of the city, listen to their stories, share yours.
We are a daily life sim, that means much of the time you can enjoy re-enacting daily life; shopping, drinking coffee on Unter Den Linden, cleaning your house, finding a job, etc.
Life can be harsh in 1929 so sometimes it is a struggle for survival.
Getting to meet as many people in the neighbourhood as possible is the best tip I can give you.
Also, we're having a Spring Ball this saturday, always a good moment to meet new people 
Berlin
April 9th 1929
You are hereby invited to the annual Sommerfrische Ball in Berlin today.
Every spring rich people prepare to leave the city and spend the summer in their country houses.
Most of us will have to spend summer in the narrow hot smelly streets of Berlin but we too celebrate this time of year with a Ball!
The Ball is today.
We will gather at Schinkelpark at 1 pm slt where we will celebrate the coming of spring with a toast from a big barrel of brand new almost cold Schnapps!
At 2 pm we all move to the prestigious Hotel Adlon in our best outfit and we dance till we fall over.
The social event of the city where you have to be seen.
Hi
Hm, i went there with a black and white retro dress and some wachtmeister told me it wasn't 20' Very weird. I came to the conclusion that the overall experience isn't really realistic.
Not because of the remark to me, but what i see is a mis interpretation. It seems a very American way of looking at it. The European 20's (Weimar) was indeed different from the American '20's look. I was informed a historic consultant had been involved. This was a bit of a surprise to me as i could not really see it.
My family is German and i am well aware of that era. Especially during that Weimar decade the women dressed very more open, the brassiere had been introduced, far above knee skirts (and even mini), fishnet nylons et cetera. Black and White dresses had been introduced from Parisien couturiers
In America, short and open dresses were less done and the more US style dressing was followed. I think it may have to do with the more puritane look at it from the other side of the pond, perhaps.
But anyway, the sim is claimed to be successful, but very strict on their way of looking at European 20's which is a bit off when it comes to outfits. The dress code is Chicago 1920, not actual Weimar 20's But perhaps it's just play there.
I could not convince the wachtmeister. Perhaps Freud was more than correct when he claimed that if people have a deep believe in something they will be hardly open for new information, specially when a consultant was hired for it. It is what i see often, specially in sl, but also rl.
Anyway, nice Sim, but realistic? No not when it comes to dressing i'm affraid. A-typical Chicago, yes.
I do wish all the best with the sim and i hope you could be more open to really real couturier trends from that particular era other than the very fixated "Chicago style" one in the project.
I am the builder of the sim and in RL I am a historical consultant for movies, tv, museums, authors, etc.
I am European and also have a German family, some of whom lived trough the 1920s, told me their stories and showed me their pictures.
My research is only based on real 1920s German information.
Over the last 2 years we have had a LOT of discussions and done a LOT of research about what kind of clothing would be authentic and realistic.
Generally we are very tolerant and sometimes look the other way when clothing is a bit too early, a bit later or sort of looks ok.
I have just read about your encounter and seen a snapshot of your outfit.
I am sorry to say I have not seen women on 1920s photos wearing outfits like yours, in Berlin, Europe or even America.
Nylon stockings didn't make it to Europe till 1945 and most women didn't even get those till the 1950s.
Just like the miniskirt.
I would have acted the same if I had encountered you myself.
The wachtmeister asked you to proof him wrong, you didn't.
Yes I know there were flappers, who sometimes dared to wear slightly shorter dresses that would show the knees, however this was only done for a very short time, skirts soon became longer again.
Of course they wore much more exciting clothes when going out or when on stage as a Siegfield Folly, but walking around the streets showing your thighs was just not very common.
Our dresscode is 1920s, we generally don't care if you wear something American or European, or even early 1930s or something a bit earlier.
The freebies and many of the shops there do however make clothes especially for the theme and the sim.
One of the best and well known vintage designers in SL, Sonatta Morales, has made several authentic dresses for our sim.
A proper couturier.
I have many 1920s Weimar images and again, no women walking around the streets showing off more then their thighs, if you have such images, I'd love to see them.
Here is a nice real 1920s Berlin photo showing Police checking two ladies to see if their dresses are not too short... I can't even see the knees.
