Calle del Cristo
Calle del Cristo (Cristo Street) is a cobblestone street in Old San Juan that has a wide variety of shops, from very touristy souvenir stores to factory outlet stores for high-end brands. Shops along Calle del Cristo include Coach, Ralph Lauren, Burberry, Tommy Hilfigger, Dooney & Bourke, Crocs, and Polo as well as local shops including a cigar shop (Don Collins), clothing stores, shoes stores, boutiques, and plenty of tourist souvenirs such as t-shirts and panama hats. There are also several art galleries, so you can pick up some local art as well as some hand-crafted Puerto Rican goods.
Calle del Cristo runs north and south starting at Parque de las Palomas on the southern end and running north to the entrance of El Morro Fort. The street has stores, restaurants, bars, art galleries, and a variety of tourist attractions including Totem Telurico in Quincentennial Plaza, San Jose Church, San Jose Plaza, San Juan Bautista Cathedral, Parque de las Palomas, and Capilla del Cristo. So, you can certainly make an entire day of visiting the shops, restaurants, and Puerto Rico Tourist Attractions along Calle del Cristo.
Taking the free trolley to the northern end of Calle del Cristo near the entrance to El Morro Fort is a good option since you will end up walking downhill and Calle del Cristo can be a bit steep, especially if you are planning to walk the entire length of the street. However, the shopping is mostly towards the southern end, so if you are only interested in shopping stay south of San Juan Bautista Cathedral which is roughly at the midpoint of the length of the street. On the southern end, you can also turn east on Calle Fortaleza, towards the cruise ship piers, and find more factory outlet stores (such as Guess) and more local shops.