Parque das Nações and Oceanário
Newest part of town, site of Expo'98. The Oceanário is Europe's biggest indoor aquarium. Admission 14€, closes at 20:00. To get there take the red line from Alameda to Oriente and then walk. [Wikipedia],[Tripadvisor], [official site](unavailable at time of writing)
Ancient castle overlooking the city center, one of the main tourist spots of Lisbon. Admission 8.50€, open until 21:00. Take the green line from Alameda to Baixa Chiado and then walk. [Wikipedia], [official site]
The part of Lisbon town closest to the Atlantic, full of monuments and museums, and pasteis de Belém. To get there take the green line from Alameda to Cais do Sodré and then take the 15E tram westward. [Wikipedia]
Visit the museum stocked with ancient and modern art, or just enjoy the park. Walk from IST. Admission: Park and some exhibitions free; otherwise around 10€. Free on Sundays after 14:00. Opening hours: 10:00 - 18:00. Closed on Tuesdays. [official site], [Wikipedia]
Hot Clube de Portugal
Best Jazz club in town. Closed on Mondays. Tuesdays at 22:30 jam session, free admission. Other nights 7.50€. Take the yellow line from Saldanha to Marquês de Pombal, take the blue line, to Avenida. [official site], [Wikipedia]
More details to follow.