If Alyona Rybnikova ever met a boy she liked, the 19-year-old would test his mettle by taking him bungee jumping at Gorky Park. ""Only a real man could do this,"" she said while peering at the four-story high ledge from where her future lover would fling his body, head down and legs tied. ""A real man should be able to do crazy things."" She has more than slim pickings to choose from since the Tarzan, as the park's popular attraction is called, lures an adventurous group of daredevils, male and female, when the weather is right. But outdoor summer fun need not mean great leaps of faith f and not every lady wants her valiant gent to fly. For many, a pleasant paddle-boat ride, a stroll down the Arbat or tanning on a nude beach will do. One summer month remains, and if the gods are kind enough to still the heavens, there will still be plenty of activities and entertainment outside those stuffy clubs and smoky bars.