Hi Agrim -
<<" I was just confused as to what places I have to avoid with my 6mth old infant.">>
There is a lot to see and do in or near Luzern. See the link provided by Lucas. Also, the tourist information office in the main station (along side the lowest numbered track (track 3?) is extremely helpful. If your child were old enough to enjoy a playground, there is a magnificent one beside the lake at the Transport Museum ( das Verkehrshaus).
There has been considerable discussion on this forum concerning taking infants (who possibly cannot communicate their distress well) to altitudes above approximately 2000 meters. There has been a wide range of opinions on this point, some of which relate not to the issue of high altitude distress but rather to the difficulty in clearly recognizing distress if a child cannot communicate clearly. I have also consulted a physician friend for perspective. Best advice is to check with your child's doctor.
I am not sure of the best way to check altitudes easily. For specific mountains you can do a Google search, and a Wiki report for a city or a mountain usually has altitudes. Google maps does not seem to routinely display altitudes.
Simply out of habit, I always use this excellent highly detailed map to check altitudes, which has tremendous detail, possibly even too much information for a simple altitude check:
map.geo.admin.ch/?topic=swisstopo&lang=e n&bgLayer=ch.swisstopo .pixelkarte-farbe&layers=ch.swisst opo.swisstlm3d-wanderwege&zoom=3&laye rs_visibility=false&E= 2674186.37&N=1199232.7 3
You can see that Pilatus at 2100 meters +/- (just southwest of Luzern), is probably tolerable by that advice, whereas Mt. Titlis, due south of Luzern near Engelberg, is well over 3000 meters. The Rigi is only about 1800 meters. Zoom in and out and play with the map.
For simple travel needs, I like this map, which sadly does not display altitude:
In that map, if you zoom in as far as zoom level 32, the train lines and mountain transport become very clear.
Both have good search functions.