To make it easier for visitors to Frankfurt, you always try the Top Things to Do in Frankfurt list.
If you want a teaser, then read on....
The first thing to know about Frankfurt is that it small is perfect - this is not a sprawling cluster of suburbia, nor a mega-city, not that Frankfurt doesn't have some of the colourful diversity that mega cities thrive on.
Frankfurt am Main is an old and established Germany city in the heart of Europe.
Most areas of Frankfurt are reachable by underground trains (U-Bahn) and buses. For Outer areas uses an U-Bahn or the over ground trains (S-Bahns).
Although the River Main cuts through Frankfurt, there are numerous bridges, including pedestrian bridges.
There are contrasting areas of Frankfurt, all easily accessible by public transport, walking, or cycling:
Frankfurt Inner City Innen Stadt: This is an international, European, and local financial hub, including the Frankfurt Stock Exchange, adjoining a massive street of shops, including multi-level department stores: Zeil. Most people are walking along Zeil and don't even know it! At the eastern end of the Zeil is the Konstablerwache Market (Farmer's Markets every Thursday and Saturday). If you are not into finance or shopping, then pay a visit to the old heart of Frankfurt with a medieval flavour: Frankfurt's Old Town. There's the old square, churches, and quant architecture (reconstructed: most of the original ornate timber work was bombed to smithereens and hence (as expected) very flammable).
Frankfurt Airport : Whether you're flying to Frankfurt or flying out, this is perhaps your first taste of proper European infrastructure: A major airport that actually works (unless there is a strike (infrequent) or some black swan causes air-travel misery like an exploding Icelandic Volcano). Once you've cleared the usually security dance and pious bow to the global protectors of the airlines, you're free to take an S-Bahn (over ground train), an ICE (Inter-City-Express - not quite a bullet train BUT faster than some light planes) or just a plain taxi into Frankfurt.
Frankfurt Messe: In Frankfurt for a trade fair? This is where you'll go to. Messe is easy to get to and easy to get out of. The Fair Halls are massive and interconnected, and there are enough sings in English to help those with even the most rudimentary of English surfacing to their mind as German confuses or just mystifies them.
Bahnhofsviertel: Home to Frankfurt's Main Railway Station (Hauptbahnhof) which is a very bustling transport node in a pan-European rail network, and Frankfurt's Red Light District; all the business activities one would expect from few blocks devoted to brothels and legal prostitution, strip clubs, bars, clubs, sex shops, and yes, multi-cultural restaurants. Well worth a visit, because it is not far away, if you are stuck at the Hauptbahnhof for a few hours.
Nord End: Where do the middle, upper-class, and uber-rich dwell in Frankfurt? Possible Nord-End. This is a stylish suburb, spared the bombing of World War Two, and still in pristine condition. Well worth a look if 1900s posh European residential architecture is your cup of tea.
Sachsenhausen: What do people in Frankfurt drink? Apple Wine. Have you ever tried Apple Wine? When in Frankfurt, maybe you should, because experience has taught yours truly that some of the fine cuisines in Frankfurt, e.g. schnitzels, roasted pig trotters (Schweine Haxe - it sounds better in German) server with sauerkraut (no wonder it's so easy to call Germans krauts and not feel racist), and meatballs (Frikadelle), need a good healthy dose of Apple Wine to wash them down with. However, failing Apple Wine, there are enough quality beers and local German white wines to satisfy the thirst of any seasoned drinker from any country that likes a drink, or two, or a whole bottle. In Sachsenhausen is a peculiar few streets packed with bars and taverns and drunkenness. If you're flying into Frankfurt and staying a few days, make the effort to pay a visit. Note: When ordering an Apple Wine, if it is for you and a special friend, or a whole gang of thirsty travellers, order a Bembel, these are the unique jugs that Apple Wine is served from.
Bornheim: The spine of Bornheim is Berger Strasse (close to three kilometres along) and conveniently split into the northern part; a bohemian enclave with feisty locals, and the southern section; gentrified yuppie utopia. There is nothing wrong with stereotypical anthropological observations, so if you have the time, explore Bornheim and find out for yourself.
Bockenheim: Home to a university, and therefore teeming with students. But don't be put off by German University students. They are very tame, a bit political and radical in a touchy feely sort of way, but since most education is free, if you leave them alone they'll leave you alone.
West End : Frankfurt's Westend is more Mayfair than Manhattan, less in your face than many a finance district yet don't let the calm surface lull you into thinking the nice new office buildings and classical villas are there to be admired as testament to a trustworthy banking era gone by. West End is the classy and sophisticated side of Frankfurt's international finance that usually goes un-noticed, mainly because it avoids publicity. Yes if you can make it in New York you can make it anywhere, but if you can make it in West End in Frankfurt, why do you care about NY, London, Tokyo or Shanghai?