Sitka’s public bus system runs on three lines and serves practically everywhere of interest to visitors. The only downsides: it doesn't stop at the airport (the last stop is about 0.75-miles short) and it doesn't run on weekends.
The green line does a loop around town. The blue line heads south via Whale Park to the Fortress of the Bear. The red line heads north to the cruise dock and the ferry terminal. Crescent Harbor serves as the terminus for all three lines.