Sergiev Posad (Russian: Сергиев Посад) is a city in North Moscow Oblast, which is famous for its Troitse-Sergeeva Monastery, the spiritual home of the Russian Orthodox Church. It is often visited as a part of the Golden Ring around Moscow.
Trains leave every 30 minutes between Sergiev Posad and Moscow's Yaroslavsky train station. The station is located at Komsomolskaya metro station (red line). A return ticket costs about 150 roubles. It is an easy day trip from Moscow.
The main tourist spot is the monastery. The train station is quite close to it and one can easily walk there in about 10 minutes.
The reason why one should see the city is the monastery. The monastery of Sergiev Posasd is one of the most beautiful monasteries in Russia and one of the principal spiritual centers of the Russian Church. It is a combination of a fortress and a monastery. The seminary of the Russian Orthodox Church is located in the buildings of the complex. There are several churches to see, a holy source and in general the whole complex with its massive walls and gates is very picturesque. There are no admission price to pay except for the museum, which shows old religious objects and woven pictures of saints. At the weekend the monastery can get very crowded, as it hosts some very important icons (at least copies of them). In return it can be very interesting to observe the believers kissing the icons and praying for hours.
The grave of Boris Gudunov (of Pushkin's play and Russian history) and some family members is also located here.
There is a restaurant called Rusky Dvornik (Russian courtier) which is quite good, but also expensive taking into consideration the general price level of Russian province. It is located just in front of the entry of the monastery.