USGS EarthExplorer — the free browser for Landsat (and many other USGS/NASA) imagery.

• URL: https://earthexplorer.usgs.gov
• Workflow: choose Search Criteria (address/coords/WRS path+row/date range) → choose Data Sets (e.g., Landsat Collection 2 Level-2) → Results → download.
• You need a free USGS account to download full scenes.
• Other sources: Copernicus Browser (Sentinel-2), Google Earth Engine (for massive time-series analysis).