Quoting directly from the information plaque at the fortress:
Built between 1622 and 1638, this fortress was, together with Mount Fortress, crucial in the protection of the city from the tentative Dutch invasion of 1622. Inside the fortress stands Guia Chapel, built around 1622 and Guia Lighthouse built in 1865, the first modern lighthouse on China's coast, still in operation to this day. Macao takes the reference for its geographic coordinates from this lighthouse. Guia Chapel is dedicated to Our Lady of Guia, noting that "Guia" means "Guidance" in Portuguese.
Options to get up here is either just walking up the streets and climbing the stairs. Or, when coming from the south, there is a combination of elevators and tunnels that reduce the climb. Or towards the northern end of the park is a ropeway. But it then requires traversing the park.