diff --git a/03_Code/off/off.py b/03_Code/off/off.py
index e10c980..5e00355 100644
--- a/03_Code/off/off.py
+++ b/03_Code/off/off.py
@@ -17,6 +17,7 @@
 # along with this program (see COPYING file).  If not, see <https://www.gnu.org/licenses/>.
 
 import os
+from pathlib import Path
 
 import logging
 lg = logging.getLogger('off')
@@ -133,19 +134,20 @@ def __dir_init__(self, settings_sim: dict):
         run_id = self.__get_runid__()
 
         try:
-            root_dir = data_dir or f'{os.environ["OFF_PATH"]}/runs/'
-            lg.info('Root runs directory: ' + root_dir)
+            root_path = Path(data_dir) if data_dir else Path(os.environ["OFF_PATH"]) / "runs"
+            lg.info('Root runs directory: ' + str(root_path))
         except KeyError:
-            if os.environ["PWD"].endswith("03_Code"):
-                root_dir = data_dir or f'{os.environ["PWD"][:-len("03_Code")]}/runs/'
+            cwd = Path.cwd()
+            if cwd.name == "03_Code":
+                root_path = Path(data_dir) if data_dir else cwd.parent / "runs"
             else:
-                root_dir = data_dir or f'{os.environ["PWD"]}/runs/'
+                root_path = Path(data_dir) if data_dir else cwd / "runs"
 
-        self.sim_dir = f'{root_dir}/off_run_{run_id}' if sim_dir is None else sim_dir
-        self.root_dir = root_dir[:-len("runs/")]
+        self.sim_dir = str(root_path / f'off_run_{run_id}') if sim_dir is None else sim_dir
+        self.root_dir = str(root_path.parent)
 
-        if not os.path.exists(self.sim_dir):
-            os.makedirs(self.sim_dir)
+        if not Path(self.sim_dir).exists():
+            Path(self.sim_dir).mkdir(parents=True, exist_ok=True)
             lg.info('Created simulation directory at ' + self.sim_dir)
 
     def __logger_init__(self, settings_sim: dict):
diff --git a/test_off_dir_init.py b/test_off_dir_init.py
new file mode 100644
index 0000000..86d704f
--- /dev/null
+++ b/test_off_dir_init.py
@@ -0,0 +1,47 @@
+import sys
+from pathlib import Path
+
+
+sys.path.insert(0, str(Path(__file__).resolve().parent / "03_Code"))
+
+import off.off as off
+
+
+def _make_off(run_id: int) -> off.OFF:
+    off_obj = off.OFF.__new__(off.OFF)
+    off_obj.__get_runid__ = lambda: run_id
+    return off_obj
+
+
+def test_dir_init_falls_back_to_cwd_when_off_path_missing(tmp_path, monkeypatch):
+    monkeypatch.delenv("OFF_PATH", raising=False)
+    monkeypatch.setenv("PWD", str(tmp_path / "not_used"))
+
+    cwd = tmp_path / "workspace"
+    cwd.mkdir()
+    monkeypatch.chdir(cwd)
+
+    off_obj = _make_off(run_id=1)
+    off_obj.__dir_init__({"simulation folder": None})
+
+    expected_sim_dir = cwd / "runs" / "off_run_1"
+    assert Path(off_obj.sim_dir) == expected_sim_dir
+    assert off_obj.root_dir == str(cwd)
+    assert expected_sim_dir.exists()
+
+
+def test_dir_init_uses_parent_when_cwd_is_03_code(tmp_path, monkeypatch):
+    monkeypatch.delenv("OFF_PATH", raising=False)
+    monkeypatch.setenv("PWD", str(tmp_path / "not_used"))
+
+    code_dir = tmp_path / "project" / "03_Code"
+    code_dir.mkdir(parents=True)
+    monkeypatch.chdir(code_dir)
+
+    off_obj = _make_off(run_id=2)
+    off_obj.__dir_init__({"simulation folder": None})
+
+    expected_sim_dir = tmp_path / "project" / "runs" / "off_run_2"
+    assert Path(off_obj.sim_dir) == expected_sim_dir
+    assert off_obj.root_dir == str(tmp_path / "project")
+    assert expected_sim_dir.exists()