A visit to Sintra is a must when exploring Lisbon. While the National Palace of Pena is one of the most visited - and therefore busiest sights, it's still a bucket list experience.
It can be accessed by train from Rossio station (Lisbon centre), which takes just 40 minutes. The easiest way to reach the palace from the Sintra train station is to take an Uber, as the Tuktuks and busses are expensive and crowded. Afterwards, we opted to walk back down to Sintra train station, which took less than an hour.
Do make sure to book your tickets online beforehand and to arrive on time. We took one of the earliest trains there and had a quick breakfast at the picturesque "Café Saudade" before heading up, which I would definitely recommend.
Even though the palace exterior is the highlight, we loved visiting the inside and see all the history too. If you have the time, make sure to explore the palace gardens as well. They are enormous and offer a nice peaceful oasis away from the masses as we were almost the only ones exploring them.