Tram travel is free throughout all of Melbourne's city centre, with "free zone" limits clearly marked at tram stops and indicated on board the trams themselves. Fare payment is required outside the free tram zone, which is done by a chargeable "myki" travel card (works on trains, trams and buses) A better alternative for short-term visitors might be a "myki Explorer" card that grants visitors unlimited travel on all forms of public transport in Melbourne for 1 full day. The "myki Explorer" also includes discounts on entry tickets to several local attractions, and may be purchased at Melbourne Visitor Centre in Federation Square, SkyBus terminals at Melbourne Airport and Southern Cross Station, PTV Hubs, and multiple hotels. Metro trains cover the city centre and suburban areas with Flinders Street Station as the main hub and run from around 5am to midnight. There are 5 central stations: Flinders St, Southern Cross, Flagstaff, Melbourne Central and Parliament. Buses cover the whole city and suburbia, and run from 5:30 am to 11:30 pm, with several routes operating throughout the night. Bike Share service is also available for those willing to explore the city by bicycle, first 30 minutes of use are free of charge but a small deposit is required. You can also use the Yarra River as a means of transportation, where boat cruises, water taxis and even gondolas will take you on board.