We stumbled across this area in shinjuku and loved it. It's a block of narrow streets crowded with shop fronts that have been turned into tiny bars. Each has its own theme from jazz to hard rock. Some enforce a cover charge but others are free. It's an interesting place for a drink.

Loved these streets with their 200+ tiny bars all stacked on top of one another. We very nearly missed it but a friend of ours took us the night before we flew home. It's kind of intimidating, but you just need to be brave and walk in your chosen bar. Most of them seem to have cover charges of about 1000 yen, but this is understandable considering how small they are (they couldn't survive if groups of tourists just came to nurse a solitary beer for 4 hours....). Make sure you pick one that looks like it welcomes foreigners, as some prefer locals or Japanese speakers due to their regular clients. We started with a great bar - it had a "welcome foreigners" sign outside which clinched it for us, and was New Mexico themed. The proprietor had excellent english and we had a good chat over a few beers. Then we headed to Bar Bran, which is upstairs on one of the outer most streets, and has cats your you to admire if you pay the 1000yen per head cover charge. Drinks aren't cheap, but you're paying for a unique experience, and we were offered snacks for free. We ended up drinking whiskey with a salaryman who wanted to practise his english, which was an awesome experience!