Cities: Skylines is a deep city-building simulation where you zone land, lay roads, manage budgets, and handle public services for a growing virtual population. Players typically start small and spend long, creative sessions expanding into massive metropolises, tweaking traffic patterns, district policies, and infrastructure while incorporating DLC content and hundreds of community mods from the Steam Workshop. The experience is open-ended sandbox play rather than story-driven or competitive, rewarding patience and experimentation over quick reflexes. Performance becomes increasingly important as your city scales. Early-game towns run smoothly on almost anything, but once population exceeds 50,000–100,000 and mods add thousands of custom props and buildings, the simulation load grows exponentially. The Unity engine's multi-core simulation handles citizen pathfinding, traffic routing, garbage collection, and service dispatching in real time; when these threads can't keep up, the in-game day slows down, commands feel laggy, and zooming or editing large areas stutters noticeably. RAM usage also climbs sharply with asset-heavy mods, frequently causing crashes if capacity is too low. Common pain points include late-game slowdowns that make detailed building frustrating, sudden frame-time spikes when new services level up, and out-of-memory errors after heavy Workshop sessions. Many players mistakenly focus only on GPU power or cheap storage, only to discover the game leaves high-end graphics cards largely idle while the CPU and memory become the real bottlenecks. Before choosing a PC, understand that this is a CPU- and RAM-first game where simulation responsiveness and large-scale stability matter more than high frame rates or ultra graphics settings.