Question: In which European mountain range will you find the mountains Grassen and Titlis both found between the cantons of Obwalden and Berne?

full_context: Document 1: Reissend Nollen: The Reissend Nollen is a mountain peak of the Urner Alps, located on the border between the Swiss cantons of Obwalden and Bern. It lies on the range west of the Titlis, between Engelberg and Gadmen.
Document 2: Generoso Vetta railway station: Generoso Vetta is the upper terminal railway station of the Monte Generoso railway, a rack railway that connects Capolago with the summit of Monte Generoso in the Swiss canton of Ticino. At 1,592 metres above sea level, it is the highest railway station in Ticino. The station is situated a short walk from the mountain summit, and only a few metres from the international border with the Italian region of Lombardy.
Document 3: Bernina railway: The Bernina railway is a single-track railway line forming part of the Rhaetian Railway (RhB). It links the spa resort of St. Moritz, in the Canton of Graubünden, Switzerland, with the town of Tirano, in the Province of Sondrio, Italy, via the Bernina Pass. Reaching a height of 2,253 m above sea level, it is the highest railway crossing in Europe and the third highest railway in Switzerland. It also ranks as the highest adhesion railway of the continent, and – with inclines of up to 7% – as one of the steepest adhesion railways in the world. The Bernina railway is also notable for its big height difference on the section between the Bernina Pass and Tirano: (1824 m ), allowing passengers to see glaciers and palm trees on the same line.
Document 4: Eibsee Cable Car: The Eibsee Cable Car, which opened in 1963, is a cable car which connects the lower station (973 m above sea level) near lake Eibsee with the top station at 2950 m above sea level next to the summit of Zugspitze, Germany's highest mountain on the border to Austria. The cable car was built to provide a faster access to the Zugspitze from its German side, as the cog railway from Garmisch-Partenkirchen does not go directly to the summit and takes much longer. The "Eibsee Cable Car" belongs to "Bayerische Zugspitzbahn Bergbahn AG", the company operating the cog railway and most cable cars, gondola lifts and chairlifts in the Garmisch-Partenkirchen area. It is thus possible to make round trips using both the cog railway and the cable car. On the Austrian side, there is the Tyrolean Zugspitze Cable Car which starts at Ehrwald and meets the Eibsee Cable Car on the top.
Document 5: Grassengrat: The Grassengrat is a multi-summited mountain of the Urner Alps, located on the border between the cantons of Obwalden and Uri in Central Switzerland. It lies on the range between the Titlis and the Gross Spannort. The main summit has an elevation of 2,941 metres and is named "Stössenstock".
Document 6: Titlis: Titlis is a mountain of the Uri Alps, located on the border between the cantons of Obwalden and Berne. At 3238 m above sea level, it is the highest summit of the range north of the Susten Pass, between the Bernese Oberland and Central Switzerland. It is mainly accessed from Engelberg (Obwalden) on the north side and is famous as the site of the world's first rotating cable car. The cable car system connects Engelberg (996 m ) to the summit of "Klein Titlis" (3028 m ) through the three stages of "Gerschnialp" (1262 m ), "Trübsee" (1796 m ) and "Stand" (2428 m ).
Document 7: Piz Platta: Piz Platta is the highest peak in the Oberhalbstein Alps. It is 3392 metres high (Source: Landeskarte der Schweiz no.1256 - 1991), and is notable for its similarity in shape to the Matterhorn. Piz Platta is located between the localities of Avers and Mulegns, both in the Swiss canton of Graubünden.
Document 8: Zugspitze: The Zugspitze, (] ) at 2,962 m (9,718 ft) above sea level, is the highest peak of the Wetterstein Mountains as well as the highest mountain in Germany. It lies south of the town of Garmisch-Partenkirchen, and the Austria–Germany border runs over its western summit. South of the mountain is the "Zugspitzplatt", a high karst plateau with numerous caves. On the flanks of the Zugspitze are three glaciers, including the two largest in Germany: the Northern Schneeferner with an area of 30.7 hectares and the Höllentalferner with an area of 24.7 hectares. The third is the Southern Schneeferner which covers 8.4 hectares.
Document 9: Grison Alps: The Grison Alps are the mountains of the Graubünden canton of Switzerland (Grisons being the English name for the Graubünden region). There are many significant peaks in the Grison Alps, including the Tödi (3,614 m) and the highest peak, Piz Bernina (4,049 m). Many of the mountain ranges feature extensive glaciers, such as at the Adula, the Albula, the Silvretta, the Bernnina or the Rätikon range. The Grison Alps include parts of both the Eastern Alps and the Western Alps. The Eastern Alps located in Graubünden are the Rhaetian Alps, which is part to the Central Eastern Alps. The Rhaetian Alps consists of the following mountain ranges: Samnaun Alps, Rätikon, Silvretta, Sesvenna Range, Albula Range, Plessur Range, Oberhalbstein Range, Livigno Range, Bregaglia Range and the Bernina Range. The Western Alps located in Graubünden, include portions of the Lepontine Alps and the Glarus Alps.
Document 10: Zugspitze Glacier Cable Car: The Zugspitze Glacier Cable Car (German: "Zugspitz-Gletscherbahn" ) is a 1,000 metre long cable car on the Zugspitze, Germany's highest mountain. It was opened in 1992 and links the plateau of the "Zugspitzplatt" directly with the summit, 360 metres higher. Since the mountain station of the Bavarian Zugspitze Railway was moved from the Schneefernerhaus to the "Platt", the Schneefernerhaus and the old cableways, which ran down into the valley from the "Platt" (the "Hangbahn" and "alte Gletscherbahn") and up to the summit ("Gipfelseilbahn"), have lost their importance.
Document 11: Bernina Express: The Bernina Express is a train connecting Chur (or Davos) in Switzerland to Poschiavo in Switzerland and Tirano in Italy by crossing the Swiss Engadin Alps. For most of its journey, the train also runs along the World Heritage Site known as the Rhaetian Railway in the Albula / Bernina Landscapes.
Document 12: List of mountains of Obwalden: This is a list of mountains of the Swiss canton of Obwalden. Obwalden is a very mountainous canton and is one of the nine cantons having summits over 3,000 metres. Topographically, the three most important summits of the canton are those of the Titlis (most elevated), the Brienzer Rothorn (most prominent) and Pilatus (most isolated).
Document 13: Wildstrubel: The Wildstrubel (3244 m ) is a mountain of the Alps, straddling the border between the Swiss cantons of Bern and Valais. It forms a large glaciated massif, about 15 km wide, extending between the Rawil Pass and the Gemmi Pass. Along with the Muverans, the Diablerets and the Wildhorn, the Wildstrubel is one the four distinct mountain massifs of the Bernese Alps that lie west of the Gemmi Pass. The massif of the Wildstrubel is at the centre between the valleys of Simmental (BE), Engstligental (BE) and the Rhone (VS), the exact location of the tripoint being the summit of the Schneehorn. It comprises several distinct summits, including (from west to east) the Wetzsteinhorn, the Rohrbachstein, the Weisshorn, the Pointe de la Plaine Morte, Mont Bonvin, the Trubelstock and the Schneehorn. The main crest with the almost equally high summits of the Mittelgipfel (3,243.5 m) and the Grossstrubel (3,243 m) forms an amphitheatre oriented eastward which ends at the Steghorn and the Daubenhorn. This area encloses the Wildstrubel Glacier. To the southwest, the Wildstrubel overlooks the high glacier plateau of the Plaine Morte, which also includes an unnamed lake below the Schneehorn.
Document 14: Grassen: The Grassen is a mountain of the Urner Alps, located east of the Titlis in Central Switzerland. The summit is the tripoint between the cantons of Berne, Obwalden and Uri.
Document 15: Uri Alps: The Uri Alps (German: "Urner Alps" ) are a mountain range in Central Switzerland and part of the Western Alps. They extend into the cantons of Obwalden, Valais, Bern, Uri and Nidwalden and are bordered by the Bernese Alps (Grimsel Pass) and the Emmental Alps to the west (the four lakes: Lungerersee, Sarnersee, Wichelsee, and Alpnachersee), the Schwyzer Alps to the north (Lake Lucerne), the Lepontine Alps to the south (the valley of Urseren with Andermatt) and the Glarus Alps to the east (Reuss).
ground_truth: Alps