Bicicleta de Utilização Gratuita de Aveiro - that can be “rented”, for free, in specific spots in the city. You just need to present your Identification Card. See the location here!
If you have friends coming to see the city, take them on a tour by Moliceiro in Ria de Aveiro. You can find countless spots in the center with companies offering this experience.
Reaching other Portuguese cities is easy and quite affordable by train. The trains to the main Portuguese cities run regularly, usually at least one per hour, sometimes more. You can find the schedule and prices online
You can reach other beaches, like S. Jacinto, by ferry-boat (from Barra only). See the schedule here.
Let's not forget the TAXI service, a transport available almost everywhere, including Aveiro. You can call to the (+351) 234 385 799 or visit the webpage taxisaveiro.pt.