This is not the Toronto diamond district/exchange, which is in TD Tower, but this old building is full of diamond/gem/precious metals/jewellery shops or wholesalers or whatever (way more places than listed on the map below). Lots of them in the basement. I've been there twice to have my watch repaired in a basement shop. The lobby and basement, both dark, are probably untouched since the 70s.
All the other shops in the basement are jewellery related with very discrete doors and signs so in that sense, this building makes sense. It's a far cry from a traditional retail jewellery store where you'd want rather fancy digs. If you care just about the gem you're buying then this place is for you. If you want the fancy experience to go with it then go to a shop in Yorkville.
Shouldn't be surprised though because that industry is very secretive. The diamond exchanges in New York and Antwerp look very interesting on the outside. IIRC, the insides can pass as glorified flea markets.
https://www.emporis.com/buildings/13...toronto-canada