Berlin's public transport system — U-Bahn (subway), S-Bahn (overground rail), trams, and buses — covers the city comprehensively and runs 24 hours on weekends. Buy a day pass (Tageskarte) or a 7-day pass at any station; they're valid across all modes. Validate your ticket before boarding — plain-clothes inspectors do check, and the fine is €60. The city is also extremely bike-friendly, with dedicated lanes throughout; rental shops are everywhere and bikesharing schemes are widely available.