One of top attractions of Malaga are the historical monuments of Alcazaba and Gibralfaro castle.
Entry fee is 2.25€ per person for one monument and 3.55€ per person for both monuments. I recommend seeing both and buying the ticket at the start to avoid lines. Gibralfaro castle is a little bit of hike but totally worth it.
The gardens are very well maintained and you get unparalleled views of the city. There are two cafes at the top to buy water or have a glass of wine. Restrooms are also available up top. There is also the Roman theater adjacent to Alcazaba which looks very nice at night.