Budapest has a well-developed and efficient public transportation system that is operated by BKK (Budapesti Közlekedési Központ). The system includes a variety of vehicle types and services that cater to both residents and visitors. Here's an overview:

1. Metro : Budapest has four metro lines (M1, M2, M3, and M4) that cover different parts of the city. The M1 line, also known as the Millennium Underground, is notable for being one of the oldest in the world and is a UNESCO World Heritage site. The metro is a fast and convenient way to travel across the city, especially for longer distances.

2. Trams : The tram network in Budapest is extensive and includes some of the busiest tram lines in the world. Trams are a popular choice for short to medium distances and offer scenic views of the city. Notable lines include Tram 4 and 6, which run along the Grand Boulevard, and Tram 2, which offers beautiful views along the Danube River.

3. Buses : The bus network complements the metro and tram services, reaching areas not covered by rail. There are both regular and express bus services, with some routes operating 24 hours a day.

4. Trolleybuses : These are electric buses that draw power from overhead wires. They operate on specific routes in the city and are an environmentally friendly option.

5. Suburban Rail (HÉV) : The HÉV lines connect Budapest with nearby suburban areas, making it convenient for commuters and those looking to explore the outskirts of the city.

6. Boats : The Danube River runs through Budapest, and there are boat services that provide a unique and scenic way to travel. These are particularly popular during the warmer months.

7. Funicular : The Buda Castle Hill Funicular connects the Buda side of the city with the Castle District, offering a quick and picturesque ride up the hill.

8. Cogwheel Railway : This is a special railway line that runs from Városmajor to Széchenyi Hill, primarily used for recreational trips.

The public transportation system in Budapest is integrated, meaning you can use a single ticket or pass across different modes of transport. Tickets can be purchased at metro stations, newsstands, or through mobile apps, and it's important to validate them before use. Overall, the system is known for being reliable, affordable, and a great way to explore the city.