There are two sides to Metro Exodus, 4A's third and probably greatest post-apocalyptic adventure - two varieties of space engaged in a hesitant dialogue. On the one hand, there are the wilds of post-nuclear Russia, absurdly splendid, absurdly deadly and moderately open-ended, from dessicated ports where beached tankers jut like dinosaur bones, to ice-locked cities whose sewers have become intestines, clogged with squirming radioactive polyps. Here, you'll act much as you do in other virtual wilderness escapades - trotting to the points of interest you've circled on your paper map, shaking down corpses for crafting resources and avoiding or murdering the many people and things who want to make soup from your thighbones.
These are spaces in which life is cheap - cheaper, certainly, than medical kits - and the risk of ambush is unrelenting. Exploring them is a breathless yet resolutely workmanlike experience, in which you'll spend a lot of time crouched in the undergrowth, wondering whether your last three shotgun shells are enough should the bandit upstairs catch sight of your weapon's laser pointer. But running through these vistas is another kind of space, in which other kinds of action - kinder actions, in fact - are possible. This is the mighty steam locomotive that carries protagonist Artyom and his comrades from map to map, as you journey eastward from Moscow's underground in search of a new home. Between lengthy stopovers in each region, usually for the sake of fuel or to deal with obstructive locals, you'll spend an interlude aboard the train - rattling past arid woodlands, poisoned waterways and wilting apartment blocks, in one of 4A's trademark masterstrokes of location design.
Each interlude corresponds to a season - Exodus's 20-30 hour campaign spans a year in-game - and it's a joy to watch those variations play out across the train's dented hull, sand caking the engine in the dry salvages of the Caspian Sea, ice brightening the fittings in the depths of winter. You can even walk along the boiler to the prow to watch the miles disappear under your feet, like Leonardo DiCaprio glorying in the view from the Titanic. But the real triumph of the train is that it's a living place, in each sense of the word - a space that evolves during the narrative as carriages are added to serve various plot purposes, and new faces join your ranks. Metro Exodus is, in this regard, both a quest for home and a story about how journeys create their destinations, as you nourish a haven whose greatest strength is that it's utterly transitory, always in motion.