The North of Spiekeroog is characterized by dunes and a sandy, high-energy, meso-tidal beach system. Seawater infiltrates in the upper beach at high tide and exfiltrates into a runnel and at the low water line during low tide. The circulating saline porewater mixes with groundwater from the freshwater lens beneath the island, producing a subterranean estuary. Research campaigns were conducted to deepen the understanding of modifications of groundwater at sediment-water interfaces as well as at redox and salinity gradients where fresh and saline groundwater mix. Within the research unit DynaDeep the campaign based site will soon become a long-term monitoring site. It is planned to install permanent monitoring infrastructure, e.g. an instrumentation platform, a camera system, and observation wells.