Sergiev Posad in russian Сергиев Посад. The city is part of the Golden Ring around Moscow.
Trains for Sergiev Posad leave all 30 minutes from Yaroslawsky train station in Moscow (same rythm at Sergiev Posad to go back). The station is located at Komsomolskaya metro station (red line). A return ticket costs about 150 roubles. It is an easy day tripp from Moscow.
The main tourist spot is the monastery. The train station is quite close to it and one can easily walk. It takes about 10 minutes.
The reason why one should see the city is the monastery. The monastery of Sergiev Posas is one of the most beautiful monasteries in Russia and one of the spiritial centres 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 complexe. There are several churches to see, a holy source and in general the whole complex whith its massiv walls and gates is very picturesque. There are no admission price to pay excpet 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 interessting to observe the believers kissing the icons and praying for hours.
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.
Trains run to Yaroslawsky Voksal all 30 minutes or even more often.