The Grand Bazaar is a great place to explore on a rainy afternoon in Istanbul. This is one of the largest and oldest covered markets in the world, with over 4,000 shops and stalls. You can find everything from jewelry and textiles to spices and souvenirs. The market is a great place to get lost in the maze of alleys and discover hidden gems. You can also stop for a cup of Turkish tea or coffee and watch the hustle and bustle of the market.