Cacilhas is located on the far bank of the river Tagus from Lisbon so unless you are a very good swimmer you'll need to get a ferry over to this town and its environs. The ferries are located at Cais Do Sodré. Take one of the orange ferries to get there, the trip only takes 5 minutes and costs €2.90 per person return. Don't worry if you just miss a ferry as they leave simultaneously from each side of the bank so there will be another coming along in just a few minutes. The ferries are very busy during rush hour as many people who work in the city commute from Cacilhas, so we suggest taking the trip out of peak hours so you can relax.
The town centre has some interesting shops and plenty of restaurants. It is worth the trip to Cacilhas and the highlight is Ponto Final for lunch. Just further on from Ponto Final is the Cacilhas Elevator, it's only €1.50 return and when you get to the top there are great views of the April 25th Bridge. 

We do not recommend Cacilhas for the evening time. 
Map Location:  Cacilhas 
There are fantastic panoramic views of Lisbon from Cacilhas