The London Institute Greenhouse
On the top of the Institute, led by a spiral staircase, the house of glass shines under the sun's rays and the moon's light. It contains dozens of plant varieties that can be used for either medical or adornment - some of them are found only in Idris. There is a little room with a set of couches and tables good for an outdoor-like picnic for the Shadowhunters. A grill is also stationed nearby, if ever anyone wants to have some grilled meat.
How about a little relaxation? Other than the library and your private room, this is a place that gives off nature's calm - a good thing whenever you're tired, or you just want to ponder on things. You can also have a little grilling party with your fellow Institute wards. A barbecue, for once in a while, is a must.