Entrance to the gardens is free, where you can walk the grounds every day of the week, except for Wednesdays. They also have free walking tours, which run about an hour, and are conducted in Hebrew, English, and Russian. During the tour, visitors learn about the design and maintenance of the gardens, as well as their significance in the Baha'i faith. In addition to the gardens, there is also shrine which visitors are free to explore.
In case you are wondering why this religious site is located in Israel... here's the story from the Baha'i website:
The Prophet-Founder, Bahá’u’lláh, was banished from his homeland and eventually exiled to Akko during the Ottoman Period. He lived in Akko for the last 24 years of His life (1868-1892), and is buried in Bahjí, in the northern part of the city. The remains of the Báb were brought from Iran and buried in Haifa in accordance with the instructions of Bahá’u’lláh, who also decided that the administrative institutions of the future Bahá’í community would have their seat on Mount Carmel.
The gardens were built to provide a fitting approach to and setting for the shrines in which the founders of the Bahá’í religion are buried. The gardens create a quiet and tranquil environment which help Bahá’ís to prepare themselves to visit their holy places.