diff --git a/core/src/uk/ac/york/student/game/activities/Activities.java b/core/src/uk/ac/york/student/game/activities/Activities.java
new file mode 100644
index 0000000..7d7eb3c
--- /dev/null
+++ b/core/src/uk/ac/york/student/game/activities/Activities.java
@@ -0,0 +1,88 @@
+package uk.ac.york.student.game.activities;
+
+import lombok.Getter;
+import org.jetbrains.annotations.Nullable;
+import org.jetbrains.annotations.Unmodifiable;
+import uk.ac.york.student.player.Player;
+import uk.ac.york.student.player.PlayerMetrics;
+import uk.ac.york.student.utils.Pair;
+
+import java.util.List;
+
+/**
+ * The {@link Activities} enum represents the different activities a player can perform.
+ * Each activity has a list of effects on the player's metrics, represented as {@link Pair}s of {@link PlayerMetrics.MetricType} and {@link PlayerMetrics.MetricEffect}.
+ * The effects of each activity are defined in the constructor.
+ * The effects are stored in an {@link Unmodifiable} {@link List}, which can be retrieved using the getter method {@link Activities#getEffects()}.
+ */
+@Getter
+public enum Activities {
+    /**
+     * The {@link Activities#STUDY} activity increases the {@link Player}'s {@link PlayerMetrics#getStudyLevel()} and decreases their {@link PlayerMetrics#getEnergy()} and {@link PlayerMetrics#getHappiness()}.
+     */
+    STUDY(
+        Pair.of(PlayerMetrics.MetricType.STUDY_LEVEL, PlayerMetrics.MetricEffect.INCREASE),
+        Pair.of(PlayerMetrics.MetricType.ENERGY, PlayerMetrics.MetricEffect.DECREASE),
+        Pair.of(PlayerMetrics.MetricType.HAPPINESS, PlayerMetrics.MetricEffect.DECREASE)
+    ),
+    /**
+     * The {@link Activities#SLEEP} activity resets the {@link Player}'s {@link PlayerMetrics#getEnergy()} and {@link PlayerMetrics#getStudyLevel()}.
+     */
+    SLEEP(
+        Pair.of(PlayerMetrics.MetricType.ENERGY, PlayerMetrics.MetricEffect.RESET),
+        Pair.of(PlayerMetrics.MetricType.STUDY_LEVEL, PlayerMetrics.MetricEffect.RESET)
+    ),
+    /**
+     * The {@link Activities#NAP} activity increases the {@link Player}'s {@link PlayerMetrics#getEnergy()}.
+     */
+    NAP(
+        Pair.of(PlayerMetrics.MetricType.ENERGY, PlayerMetrics.MetricEffect.INCREASE)
+    ),
+    /**
+     * The {@link Activities#EAT} activity increases the {@link Player}'s {@link PlayerMetrics#getHappiness()}.
+     */
+    EAT(
+        Pair.of(PlayerMetrics.MetricType.HAPPINESS, PlayerMetrics.MetricEffect.INCREASE)
+    ),
+    /**
+     * The {@link Activities#ENTERTAIN} activity increases the {@link Player}'s {@link PlayerMetrics#getHappiness()} and decreases their {@link PlayerMetrics#getEnergy()}.
+     */
+    ENTERTAIN(
+        Pair.of(PlayerMetrics.MetricType.HAPPINESS, PlayerMetrics.MetricEffect.INCREASE),
+        Pair.of(PlayerMetrics.MetricType.ENERGY, PlayerMetrics.MetricEffect.DECREASE)
+    );
+
+    /**
+     * The effects of the activity on the {@link Player}'s metrics.
+     * Each effect, in the {@link Unmodifiable} {@link List}, is represented as a {@link Pair} of {@link PlayerMetrics.MetricType} and {@link PlayerMetrics.MetricEffect}.
+     */
+    private final @Unmodifiable List<Pair<PlayerMetrics.MetricType, PlayerMetrics.MetricEffect>> effects;
+
+    /**
+     * Constructs a new {@link Activities} enum constant with the specified effects.
+     *
+     * @param effects the effects of the activity on the {@link Player}'s metrics
+     */
+    @SafeVarargs
+    Activities(Pair<PlayerMetrics.MetricType, PlayerMetrics.MetricEffect> ... effects) {
+        this.effects = List.of(effects);
+    }
+
+    /**
+     * Returns the {@link PlayerMetrics.MetricEffect} of the activity on the specified {@link PlayerMetrics.MetricType}.
+     * This method iterates over {@link Activities#effects}.
+     * If a {@link PlayerMetrics.MetricEffect} with the specified {@link PlayerMetrics.MetricType} is found, the {@link PlayerMetrics.MetricEffect} is returned.
+     * If no {@link PlayerMetrics.MetricEffect} with the specified {@link PlayerMetrics.MetricType} is found, null is returned.
+     *
+     * @param metricType the {@link PlayerMetrics.MetricType} to get the {@link PlayerMetrics.MetricEffect} for
+     * @return the {@link PlayerMetrics.MetricEffect} of the activity on the specified {@link PlayerMetrics.MetricType}, or null if no {@link PlayerMetrics.MetricEffect} is found
+     */
+    public @Nullable PlayerMetrics.MetricEffect getEffect(PlayerMetrics.MetricType metricType) {
+        for (Pair<PlayerMetrics.MetricType, PlayerMetrics.MetricEffect> effect : effects) {
+            if (effect.getLeft() == metricType) {
+                return effect.getRight();
+            }
+        }
+        return null;
+    }
+}
diff --git a/core/src/uk/ac/york/student/player/PlayerMetrics.java b/core/src/uk/ac/york/student/player/PlayerMetrics.java
index b0c271b..2329f02 100644
--- a/core/src/uk/ac/york/student/player/PlayerMetrics.java
+++ b/core/src/uk/ac/york/student/player/PlayerMetrics.java
@@ -13,6 +13,27 @@
  */
 @Getter
 public final class PlayerMetrics {
+
+    /**
+     * The {@link MetricType} enum represents the types of metrics related to a player.
+     * It includes {@link MetricType#ENERGY}, {@link MetricType#HAPPINESS}, and {@link MetricType#STUDY_LEVEL}.
+     */
+    public enum MetricType {
+        ENERGY,      // Represents the energy level of the player
+        HAPPINESS,   // Represents the happiness level of the player
+        STUDY_LEVEL  // Represents the study level of the player
+    }
+
+    /**
+     * The {@link MetricEffect} enum represents the possible effects on a player's metrics.
+     * It includes {@link MetricEffect#INCREASE}, {@link MetricEffect#DECREASE}, and {@link MetricEffect#RESET}.
+     */
+    public enum MetricEffect {
+        INCREASE,    // Represents an increase in a player's metric
+        DECREASE,    // Represents a decrease in a player's metric
+        RESET        // Represents resetting a player's metric to its initial value
+    }
+
     /**
      * The energy metric of the player.
      */