Exact location: https://plus.codes/8CCGPRPW+WF
In the grassy hill over the the lake, close to "Cafetaria do Museu Gulbenkian".
Look for a woman wearing a red shirt and a wide-brimmed hat.
Edit: The weather forecast is that it will be really hot/sunny, so we might not be in the spot above, but in some shadier place nearby. Give me a call or send me an e-mail if you're not able to find us!