Route 209 was largely a remnant of former U.S. Route 80. The Cabrillo National Monument served as the western end of this long transcontinental route.
Entire route. [CS&HC Sec. 263.1]
At the southern end is the Cabrillo National Monument, which features its own lighthouse. According to Andrew Field, "[t]his lighthouse used to warn mariners of the rocks at the shore of Point Loma in the late 1800s/early 1900s. The lighthouse and the peninsula are often shrouded in fog. Today the lighthouse is open to the public to show how life was in those days." Also along Route 209 is the Fort Rosecrans National Cemetery. The Gate at the Fort Rosecrans Military Reservation is open daily from 8:00am to 5:15pm.
If you continue north on Rosecrans, passing under Route 5, you will come across the Old Town San Diego State Historic Park. From the website: "Old Town San Diego State Historic Park recreates life in the Mexican and early American periods of 1821 to 1872. Five original adobes are part of the complex, which includes shops, restaurants and a museum." A transit center with access to Coaster trains and the San Diego Trolley (see San Diego MTS) is nearby. For more information, call (619)220-5422.
Andrew Field has a more detailed web page on Route 209, with lots of pictures, here.