Ramble through downtown San Diego on foot, eyeing urban trees and a forest of construction cranes.

Startling changes seem to be occurring at an ever-increasing pace in downtown San Diego -- or "Centre City" as it is sometimes known. Back in 1972, when I first arrived, I'd bicycle over from San Diego State College to race up and down the one-way streets, just for the fun of trying to keep up with the synchronized traffic lights. Early on Sunday mornings, nary a moving vehicle plied these three-lane streets, and the typical live humans I saw were drunks staggering from doorways in the area now known as the Gaslamp Quarter.

Sunday mornings are still relatively quiet around Centre City. They're perfect for taking the following roughly circular trek of approximately four miles, on foot preferably, for the purpose of scoping out the recent changes going on down there. It doesn't hurt to repeat the same walk every year or two -- just to marvel at the rapidity of those changes.

Start walking from a point along Cedar Street, at or near Pacific Highway (in front of the County Administration Center), or farther east, where curbside parking is free and probably abundant on Sunday mornings. According to an early 20th-century city plan, a grand promenade along Cedar Street was supposed to link Balboa Park and the bay. That never happened, but future redevelopment of the County Administration Center will include a more friendly pedestrian connection along Cedar Street between the government complex and the Harborview/Little Italy neighborhood.

Head west on Cedar, swing behind the County Administration Building, and cross Harbor Drive to get to the Embarcadero waterfront path. From now until November, an eye-catching installation of 30 sculptures collectively titled "Urban Trees" has sprouted in large flowerpots lining the Embarcadero from the foot of Hawthorn Street to the Broadway Pier. For a preview of each work see thebigbay.com/urbantrees/.

Where tuna boats once berthed along the Embarcadero docks, the obvious focus today is tourism. You pass the Star of India and other craft associated with the San Diego Maritime Museum, cruise ships large and small, and finally the giant Midway aircraft carrier museum. Inland, the vista is dominated by construction cranes and new condominium towers that increasingly are dwarfing old landmarks such as the Santa Fe railroad station.

As you approach Seaport Village, either wander through it or swing left following the sidewalk of Harbor Drive. On the latter route, you'll pass the crumbling old San Diego police station and the twin Hyatt towers. Plenty of changes are due here over the next several years as the Port District implements a nearly half-billion-dollar plan that will preserve the old station and completely reconfigure the waterfront west of there.

As you reach the near end of the convention center, cross Harbor Drive (go over to the northeast side), and continue strolling on the Martin Luther King Promenade, alongside the trolley tracks. The recently opened Petco Park baseball stadium is right ahead. Swing around the perimeter of Petco Park (tours are available, from the south entrance), using Park Boulevard and Tenth Avenue. As you curl around to the stadium's east side, marvel at the pace of construction activity that will completely change the face of the East Village section of downtown within the next few years.

Once you're past Petco Park, zigzag your way north and west back to your starting point, using any combination of north-south-oriented numbered streets and east-west-oriented lettered streets. The "lettered" streets you cross heading north are K, J, Island, Market, G, F, E, Broadway, C, B, A, Ash, Beech, and Cedar. The rectilinear plan of downtown San Diego's streets features rather wide one-way streets and smaller blocks as compared to most inner cities. There are 14 blocks to the mile in the north-south direction, and 19 blocks to the mile in the east-west direction.