Cheap nice holiday destinations from London in September?

Belgrade? It's great. Cheap, lively and the people are friendly.

I don't know if it counts as "off the beaten path," but I hear that Berlin is quite affordable, and you can certainly see some great art and have some tasty beers there.

Portugal, good night life in Lisbon and elsewhere, lots of histroical/cultural places to visit, plenty of undeveloped off the beaten track places within a couple of hours drive (or less), lots of unspoilt, undeveloped, often deserted beaches with blue seas, some nature reserves, you can do accommodation on the cheap if desired in cheapo pensions or camping, decent likelihood of good weather. We were there last year and you can do a big meal with drinks for £20 a head easy. Easy to stay away from the Brit tourist areas and so long as you do you will barely hear English, there are plenty of resorts that aren't frequented by non-Portuguese.

You want Istanbul. Great food, smoke some hooka, check out the bazaar and the mosques (gorgeous!) and the city has one hell of a club scene. Then in the morning you can recover with a hammam. And if you cross the Bosphorus and have a great fish lunch along the way, you can do 2 continents on your trip.

2nd-ing Berlin, cheap to get to, cheap to stay and a very relaxed atmosphere.

If you're looking for cheap flights, use http://www.kayak.co.uk, it searches across multiple airlines, weekends, cities and everything else, and I've nearly always saved 25 - 50% off the price of tickets compared to when I used to manually search a load of different sites. Will be following this thread with interest, always looking to add places to my list of 'places I can get to and hang out in for not much cash from London'.

Valencia or Barcelona or both. Flights are dirt cheap with Ryanair (£5 sale on at the moment,) plenty of culture, plenty of bars plus hot weather, access to beaches and other holidayish stuff.

Poland! Krakow is amazingly historic and was spared major architectural damage during the Second World War, and though it's the height of summer right now, going during the week would be quieter. Schools and unis here start up in late September, so the tourist hordes will have mostly departed. http://www.flickr.com/photos/kolouker/3002424468/ In addition to being the cultural capital of Poland, seat of the Polish crown for hundreds of years, and full of amazing bars and cafés, Krakow is near http://en.wikipedia.org/wiki/Nowa_Huta, one of only two completely-constructed Socialist Realist cities in the world, a giant salt mine at http://en.wikipedia.org/wiki/Wieliczka_Salt_Mine with a huge chapel carved out of the middle of it, and the http://www.wck.wadowice.pl/Informacja-turystyczna.15.0.html?L=1 of Pope John Paul II, which you can reach on the http://pl.wikipedia.org/w/index.php?title=Plik:Poci%C4%85g_papieski_na_stacji_Choszczno.JPG&filetimestamp=20090616171527. :) Warsaw, alternatively, was completely leveled during the Second World War (http://en.wikipedia.org/wiki/File:Destroyed_Warsaw,_capital_of_Poland,_January_1945.jpg) and then rebuilt, the Old Town so well that the reconstruction received UNESCO World Heritage Status in the 1970s. The city's museums and monuments are powerful and the city has this amazing clash of medieval, post-war concrete, and gleaming skyscrapers. It's pricier than the rest of the country, but not horrifically so. Combining both cities - as different as chalk and cheese, mind you - would be great; they're less than three hours apart on the best trains in the country. Wrocław, Gdańsk, and Toruń are more minor centers but are still packed with culture and cafés; Toruń is a bit smaller than the other two - a good overnight trip from Warsaw - and is the home of Copernicus and 40,000 students as well as being incredibly gorgeous at night, as its red-brick buildings are illuminated. A lack of Polish-language knowledge is absolutely not a problem in these cities (I lived in Toruń last year and only know a tiny amount), though a few pleasantries are always good measure. It can often be cheaper to hire a flat, even for a few days, than stay in a hotel - I'm planning to visit both Warsaw and Krakow this September with another person and the trip would be unaffordable otherwise. TripAdvisor has good recommendations, usually, with reviews from people who've actually stayed there. Hostels are everywhere too; locally-owned ones which are run by the http://obiekty.pttk.pl/start.php?jezyk=e (which also runs hotels - they're sort of a quasi-official tourism-promotion board for both cities and the countryside) can be extraordinarily good value. Alternatively, Kiev, Lviv, and Odessa in the Ukraine would be devoid of stag parties, but are quite distant from each other. Sofia and Plovdiv, Bulgaria, are only a few hours apart by train. Sarajevo, Thessaloniki, Belgrade. All the cities I mentioned have a locally-produced http://www.inyourpocket.com guide, which is updated seasonally or even more often - I lived in Riga, Latvia in 2008 and it was indispensable, miles beyond major guidebook coverage, and cheap as a paper copy locally or FREE online. They are all also outside the Euro zone, so your pound goes further (sighs a guy who earns in złoty...). :) http://www.skyscanner.net can help you search for flights to a whole country: put in "LON" - that's all London airports in the "from" box, and "Poland/Bulgaria/Ukraine" in the "to" box.

Definitely Berlin. Such a great city.