This classic map has underwent several changes since its debut with Splatoon's release, but remains a compact yet simple map with few gimmicks.
Layout
The spawn point of Urchin Underpass is fairly complicated despite being a usually neglected area. It is a large, enclosed area with several slopes descending to the lower floor, as well as grates leading away from it. The area around the spawn is a high, wide level with railings surrounding the edges, and the only way up is through the winding ramp situated at the corner in front of the spawn point. The spiral ramp also has a walkway that leads to an alternate entrance in to the main arena.
Dropping down to the lower floor, the path toward the center of the map splits. One is an elevated path partially protected by railings and hard to reach for the enemy team, while the other is behind a grated wall squids and ink can easily pass through, but solid objects like bombs can't. A pillar juts out where the split paths converge, and is tall enough that only players from the upper level can jump to. Beyond the pillar is a steep ramp leading to a side area that functions as the team's battlements. There are large patches of uninkable ground as well as two openings that make for popular sniper outposts. The opening closer toward the middle has an inkable wall so that anyone from below can swim up to it.
A large multilayered hill marks the entrance to the center, while a narrow alley runs beside it. At the end of the alley is a small flat square, and beyond that is the frontlines where shots are traded, which has a ramp for daring jumps into enemy territory, a wall for cover and two ramps leading down into the gorge between either team's concrete platforms. The platform walls are all inkable, allowing for surprise attacks from within the gorge. Two trees are placed at either end of the gorge for cover.
Mode strategies
Turf War
In Turf Wars, Urchin Underpass is a very open map due to its wide central region and myriad of paths to approach the enemy side. The spawn area has a lot of space that is unlikely to be inked by enemies except by Inkstrikes, making them ideal for Sprinkler spots at the start of the match. The pit in front of the spawn area is another good Sprinkler spot to charge your special while you proceed to the center. One more notable Sprinkler spot is the metal beam running over the gorge at the center which is both hard to destroy for some weapons and continuously inks a contentious area.
The number of paths and positions at the center makes the battle quite varied depending on team composition. The ledges forming the gorge in the middle is a good spot for frontline, ranged weapons with good sight lines for firing into the enemy side and respond to attacks from the side. While it's fairly exposed, there is a wall to provide some cover against enemy fire. The side paths and the gorge at the very center is the battleground for aggressive flanking weapons. Being boxes in from both sides limits your options for a safe retreat, though the trees on either side gives decent cover. The ramp on the enemy's right is a good flanking route since you're slightly obscured while climbing it, and puts you to the side of foes fighting at the ledge for sudden sneak attacks. Swimming up the walls of the gorge can also surprise enemies and can be deadly if your weapon can kill quickly, but it also puts you right in front of your targets' crosshairs and leaves you easily surrounded.
Chargers and other long-range weapons like to stay around the large ramp next to the battlements on the allied left side of the map. It gives a wide view of your team's side making it a strong spot for defensive sniping, and there's lots of space to move around or retreat when enemies approach. The battlements themselves are another staple sniping spot that covers the ledge and the gorge, though annoyingly the trees can block your shots. It is very safe from ambushes as enemies have limited ways of reaching you, the most straightforward of which involves swimming up a wall to the side of the gorge in full view of both the sniper and any players fighting at the center. The corridor that runs through the battlements is also narrow which limits the mobility of a flanker.
Due to the open nature of the center, one team can occasionally push quite far in to the opposing side. This push generally stops in front of the unclimbable ledges or the pit in front of spawn. This is the ideal spot for the losing team to mount a comeback, as you have a significant height advantage and the enemy is forced to fight in a narrow bottleneck. This is the best spot to pick off enemies and force a retreat so your team can gain some map control and even the scores.
Splat Zones
The single Splat Zone is snugly placed in the gorge, terminating near the two trees. Two low boxes have been added near the trees for additional cover.
Urchin Underpass's zone is situated in a hazardous and claustrophobic valley, and it is small compared with the zones on other maps, so it is inadvisable to fight on the zone itself as our dying explosion of ink can give a lot of capture progress for the enemy team. Weapons that dump ink downward, such as rollers and sloshers, are well-suited for covering the zone from the flat platforms that form the valley around it. Sprinklers are a major nuisance on this map as they can be thrown on to the beam that stretches over the splat zone, continuously raining ink on to the zone while being difficult to destroy.
Tower Control
The tower begins at the very center between the two small ramps of either team. It moves to the square and into the alley beside the hill. It continues to follow the path into the enemy base and comes to a stop at the winding ramp. The exit near the winding ramp now has an inkable block placed on the opposite side to give attackers another path to approach.
The tower's starting position is in a very chaotic spot, right in the valley with the platform roughly level to either team's ramps. It's pretty easy to get on to the tower where it initially rests but you're likely to get taken out due to being right at the center of battle at ground level with little cover. Since enemies may come from the front and even the sides through the valley, the tower isn't going anywhere until you've beaten back the enemy team a bit. Even then, the first 20 units of the journey takes place on a flat plain where enemies can easily surround you, but also allows you freedom to escape off the tower and engage the enemy team.
Around the 70 point mark, the tower passes by the tall ramp where the defenders get their first big terrain advantage in the form of high ground relative to the tower. The lone pillar and the ledge behind it lets the defending team fire at the tower with relative safety, while the ramp beside the tower lets enemies with less range attack players on the tower without having to climb on to the tower or firing at it a low angle. Control of this ramp is key as it forces the enemy team into the narrow choke the tower goes through, especially on the attacking side. At this point, the defending team's flank routes become more effective as the focus of the battle shifts inward from the center.
Progress is going to be slow beyond the 50 point mark. Once the tower ascends beyond the ledge by the tall column, it is briefly very hard to reach for the attacking team if they weren't on the tower already, due to the uninkable walls of the ledges. This forces any stray attackers to circle around through the path with the grate wall to reach the tower and continue the push, while the defense has a solid height advantage along the tower's path which is safely reachable from spawn. There is a climbable wall added to help attackers get on the path above the goal and break up the defense, but taking this path leaves you heavily exposed right in front of the enemy's spawn.
Rainmaker
The Rainmaker's initial position is at the center of the gorge, while the goal is on top of the winding ramp in front of spawn. An inkable block has been added at the split paths beside the pillar so that players can easily reach the higher path. There is another block placed beyond the grated wall to give another way on to the walkway at the top of the winding ramp.
Due to the layout of the map, there aren't many options for the Rainmaker carrier to travel toward the goal as all possible paths generally converge early into a single direction. That said, the map is open enough that the Rainmaker carrier still has a good chance of slipping past or breaking through the opposition. The addition of a climbable wall in front of spawn is the change to the map that gets the most use, routinely used as a more direct route to the narrow flank path leading to the center.
As in every map, it's ideal to break the Rainmaker's shield only after winning the initial clash, since you either have to be on the exposed platform or the low valley to fire on the shield making the prospect risky with enemies around. However, the expanded bubble shield can block enemy shots across the valley, and the threat of the explosion can force foes to retreat briefly, at least out of the valley.
Once you've secured the Rainmaker, it's simply a matter of sprinting into the enemy base. It's easier said than done, since the defending team can use the high ledges and pillar to fire with near impunity and stop the carrier's advance. The Rainmaker's range and fearsome power helps with clearing out defenders up high, but the carrier will need space to charge up shots while being quite exposed to fire at them. Alternatively, you can take the path through sniper balcony, but while it is hard for enemies to reach you here due to the limited ways on to the path and the narrow corridor, it's a bad route to gain objective points since it only counts down to 90 by the time you reach the grate on the ramp. Incidentally, these properties make the sniper battlements a great place to stall the timer if you have the lead when the match is nearing its end.
Pushing into the alleyways is a dangerous task. The pillar and wall can provide cover to the attackers from foes on the ledge to the right, but the grate forces you to hop through it while in squid form, during which you are much easier to hit and take out. The narrow alley can be used to your advantage here, as there is less room for the defense to evade Rainmaker shots within the path itself. You can also choose the higher route to the right of the path with the grate wall. Hugging the wall here gives protection from foes directly overhead, but defenders can always jump down to engage you directly.
The winding climb to the goal is the last challenge of the journey. It gets a bit awkward for the defenders to shoot at the carrier due to the layout of the spawn area, but nevertheless it's still a literal uphill climb for the carrier. The inkable block here comes into play at this point for the attackers, creating a more direct but also more exposed way on to the platform with the goal.