Rouge 98 does not accept reservations. Walk-ins are welcome.   Those three magic words in real estate can go double for restaurants. Sometimes, it really is all about location, location, location. And few dining nooks in town are better situated than Rouge, Rittenhouse Square’s cozy and personality-rich bistro. Grab a table by the window (or better yet, a rattan chair on the sidewalk under the striped awning) for optimal people watching and park views. The bar—an elevated, intimate circle that always feels like party—is another choice spot. Luckily, Rouge’s dainty size means you’ll feel included in the fun wherever you sit.   Walls are swathed with velvety fabrics, and the semi-circular booths lend themselves to lounging. Soft lighting gives patrons an attractive glow. It’s the type of restaurant you’d happily cocoon yourself in for a lazy afternoon or late evening, sipping one too many glasses of good wine and flirting innocently with a stranger. The menu says “bistro” just as loudly and the atmosphere. Red meat is among the kitchen’s strengths. The steak tartare is a classic, the rich raw meat bound with a salty aioli and eaten on thin, crisp slices of baguette. Steak frites comes cooked to a perfect medium-rare next to a mountain of excellent French fries. Of all the burgers in Philadelphia, Rouge’s is among the most famous: a thick beef patty topped with Gruyere and caramelized onions, served on a slightly sweet challah roll. Its virtues have been justifiably extolled in glossy publications local and national. But Rouge is more than its menu. Opened in 1998, long before the bistro trend blew through, it’s now an institution. It’s Rittenhouse Square’s boozy clubhouse. Like their many regulars, regardless of what you eat, you’ll want to go back for more.