diff --git a/router/handlers/simulate.go b/router/handlers/game.go
similarity index 100%
rename from router/handlers/simulate.go
rename to router/handlers/game.go
diff --git a/router/handlers/mode.go b/router/handlers/mode.go
new file mode 100644
index 0000000..dbe547c
--- /dev/null
+++ b/router/handlers/mode.go
@@ -0,0 +1,22 @@
+package handlers
+
+import (
+	"html/template"
+	"net/http"
+)
+
+type ModeHandler struct {
+	Tmpl *template.Template
+}
+
+func (m *ModeHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	data := struct {
+		Title string
+	}{
+		Title: "Title",
+	}
+
+	if err := m.Tmpl.ExecuteTemplate(w, "game-mode.html", data); err != nil {
+		http.Error(w, "Template Error", http.StatusInternalServerError)
+	}
+}
diff --git a/router/handlers/simulation.go b/router/handlers/simulation.go
new file mode 100644
index 0000000..532124a
--- /dev/null
+++ b/router/handlers/simulation.go
@@ -0,0 +1,49 @@
+package handlers
+
+import (
+	"encoding/json"
+	"net/http"
+	"systemdesigngame/internal/design"
+)
+
+type SimulationHandler struct{}
+
+type SimulationResponse struct {
+	Success  bool                   `json:"success"`
+	Metrics  map[string]interface{} `json:"metrics,omitempty"`
+	Timeline []interface{}          `json:"timeline,omitempty"`
+	Error    string                 `json:"error,omitempty"`
+}
+
+func (h *SimulationHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodPost {
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	var design design.Design
+	if err := json.NewDecoder(r.Body).Decode(&design); err != nil {
+		http.Error(w, "Invalid design JSON: "+err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	// TODO: Run simulation engine here
+
+	// For now, return a mock successful response but eventually, we want to go to the results page(s)
+	response := SimulationResponse{
+		Success: true,
+		Metrics: map[string]interface{}{
+			"throughput":   250,
+			"latency_p95":  85,
+			"cost_monthly": 120,
+			"availability": 99.5,
+		},
+		Timeline: []interface{}{}, // Will contain TickSnapshots later
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	if err := json.NewEncoder(w).Encode(response); err != nil {
+		http.Error(w, "Failed to encode response", http.StatusInternalServerError)
+		return
+	}
+}
diff --git a/router/router.go b/router/router.go
index 38f786a..0fc8d1b 100644
--- a/router/router.go
+++ b/router/router.go
@@ -12,7 +12,10 @@ func SetupRoutes(tmpl *template.Template) *http.ServeMux {
 	mux := http.NewServeMux()
 	mux.Handle("/static/", http.StripPrefix("/static/", http.FileServer(http.Dir("static"))))
 	mux.Handle("/", &handlers.HomeHandler{Tmpl: tmpl})
+	mux.Handle("/mode", auth.RequireAuth(&handlers.PlayHandler{Tmpl: tmpl}))
+
 	mux.Handle("/play/", auth.RequireAuth(&handlers.PlayHandler{Tmpl: tmpl}))
+	mux.Handle("/simulate", auth.RequireAuth(&handlers.SimulationHandler{}))
 	mux.HandleFunc("/login", auth.LoginHandler)
 	mux.HandleFunc("/callback", auth.CallbackHandler)