The Pushkin Square underpass is the busiest of its kind in Moscow. It contains the entrances to the Pushkinskaya, Tverskaya and Chekhovskaya metro stations, which are used by on average 120,000 passengers daily.
It also crosses Moscow's principal thoroughfare, Tverskaya, at its busiest point catering to tens of thousands of pedestrians. In addition, the complex underpass is filled with small shops and kiosks.
Connections to two of Moscow's most upmarket shopping arcades, Pushkinsky Passazh and Galerea Aktyor, as well as its proximity to the city's main McDonalds fastfood restaurant add to the huge congestion of people in the area for most of the day.
The underpass is situated about 800 metres north of the main entrance to Red Square, and its choice by bombers at the height of the evening rush hour indicates that the intent was to inflict the largest possible number of casualties.
It is an underpass that is very familiar to this correspondent and one which I use daily when in Moscow.
I was last there on Sunday looking at a stall that offers a large selection of CDs and would have used the underpass at least a dozen times in the past week before returning to Ireland.
From my knowledge of the place, it seems amazing that the casualty figures have not been higher.
There have been a number of bombs in Moscow in the past year, all of which have been blamed on terrorists from the breakaway region of Chechnya.
About 200 people lost their lives in two apartment block blasts in September of last year in the distant working-class suburbs of Pechatniki and Kashirskoye Shosse.
A bomb exploded on the metro between Tulskaya and Nagatinskaya stations in southern Moscow in the lead-up to the presidential election in 1996, killing four people, but yesterday's explosion, in one of the busiest parts of the city centre, is likely to have a much greater impact on Muscovites.
The Pechatniki and Kashirskoye bombs have been blamed on Chechen separatists, although none of the perpetrators have been apprehended.
Russians had been expecting some form of terrorist attack to mark what Chechens describe as the "independence day of the Republic of Ichkeria" and the anniversary of the outbreak of the current conflict a year ago.
The atmosphere in Moscow had been tense in the past week, but when the anniversaries passed without incident at the weekend, most people assumed that the danger no longer existed.
