Though being a very important mountain it almost can't be seen from the surrounding valleys : its whole splendour appears only from the East side (Alpe Veglia - Italy) with its 1300m high wall and from the West (from the ridge on the W side of Simplon pass)
The whole S side can be seen only from far away, some summits (Hubshhorn and Breithorn) hide it and the road of Sempione, in the S part, runs along a very deep and narrow valley (Gole di Gondo)
The N side can be seen from the summits N of the Bocchetta d'Aurona
But when you get the summital ridge, or, better, the summit, you can see the whole Western Alps chain.
Monte Leone is not an important alpinistic summit, no classic famous rock or ice routes, is just one of the best Easy mountaneering and ski-mountaneering summit of the Alps : the downhill from Breithorn pass to Simplon pass is very similar to the Gran Paradiso's one.
The access to the mountains start, of course, from the two opposite sides of the high ridge :
Along the Simplon highway in Val Divedro - exit for San Domenico - car parking, with a not tiring walk you can arrive to the Alpe Veglia (Small Hotels and Refuges)
If you want to climb the summit from this side you have to climb for 1850m of difference in elevation !!!
No halfway refuges but the Bivacco Farello (near the Bocchetta d'Aurona - 2770m)
Along the Simplon road up to the Simplon pass (2005m) where some (NOT cheap) Hotels and the famous and cheap Hospice can host you
From this side the difference in elevation is ~ 1500m but you can also use the Monte Leone hutte (2848m)
Public services both from Domodossola (Italy) and Brig (Switzerland) allow the access to Simplon pass from the Simplon railway stations