The market for large bank deposits traditionally operates through private channels between banks and firms, unlike the open retail deposit market. This setup makes it an opaque market for market participants and an inconvenient one to study due to limited data availability. We contribute to this underexplored area by examining the dynamics of an online deposit platform, where banks must disclose deposit offers' terms and firms can browse and select suitable offers. We find that risk and return trade-offs crucially drive market behavior: bank risk levels dictate both banks' offered rates and depositors' cash allocation, and there is no evidence of relationship banking—depositors diversify risk by depositing to several banks with attractive rates. This type of marketplace opens a channel for banks to reach new clients while creating an accessible and informative market for depositors, promoting innovative alternative markets for large deposits.